Multitasked Conversation

Bob is talking (or desperately trying to convey information) to Alice, in the presence of Charlie. Charlie doesn't know Alice is there (she's hiding, or on the other end of a hidden microphone, or a Spirit Advisor or other invisible being) or doesn't know that anything is wrong. So Charlie interprets everything Bob says as though it's being said to him, not to Alice.

Sometimes Bob has to choose his words carefully, so as to get across his meaning to Alice without blowing her cover or appearing insane. Sometimes, Bob just talks naturally to Alice, and Charlie misinterprets what Bob is saying as applying to him. Doubly difficult if Bob can't or won't lie in front of Alice or Charlie.

Compare Talking Through Technique, where Bob can talk to Alice via chess, while talking verbally to Charlie. Subtrope to Double Meaning.

Anime

 * In Death Note:
 * Shinigamis can't be seen by anyone other than the humans who touch their Death Note. This includes surveillance equipment. When Light is under surveillance by the police, he pretends to do his homework, and can only respond to Ryuk by saying things ostensibly to himself, like "I got this question right!" to indicate a "yes" answer.
 * Misa does this too, talking as if asking her captors to kill her because she can't stand the torture any longer, while actually telling Rem, her Shinigami, to kill her so that she won't break down and reveal secret information.
 * Also when Matsuda is caught. He takes cues from L over the phone to let them know he's in trouble while making it sound to his captors like he's just turning down an offer to hang out with his friend.
 * In an early episode of Nyan Koi, Junpei attempts to tell Kaede, the girl he has a crush on, that she should stop being so rough with the local cats while said local cats are chattering at him. He can't hear what she's saying, and he finally bellows 'Would you just shut up!' at the cats; cue Kaede running away.
 * The first episode of Tasogare Otome X Amnesia has one between Momoe (who can't see or hear ghosts), Teiichi (who can), and Yuuko (a ghost). Thus, Momoe interprets some of the things Teiichi says to Yuuko or his reactions to Yuuko's antics as him reading her thoughts. It gets even better when Kirie (who can see and hear Yuuko) joins in and snaps at Yuuko for her flirtatious antics, which Momoe misinterprets as being directed at her.

Film

 * In the Peter Jackson film The Frighteners, Michael J. Fox's character can see and talk to ghosts. This leads to many Multitasked Conversations throughout the movie.
 * All of Me.
 * The recent comedy Ghost Town also involves someone who can see and talk to dead people, and it too uses this trope a few times.
 * At the climax of In the Line of Fire, Leary has Frank at gunpoint in a glass elevator. Frank keeps telling him to go ahead and shoot -- but he's really speaking into a communicator concealed in his hand, to the secret service snipers, which Leary doesn't realize until Frank tells the snipers to "Aim high" (he's kneeling while Leary's standing).
 * Hogarth saying grace at the dinner table in The Iron Giant doubles (rather clumsily) as an attempt to shoo away the Giant's hand before his mom sees it.
 * Subversion: the fact that Haley Joel Osment's character doesn't talk to Bruce Willis when anyone else is around is a major clue to the twist ending of The Sixth Sense.
 * In Air Force One, President Marshall finally gets through to the White House phone line, but is cornered by one of the terrorists. He hides the phone in his pocket, and in what appears to be idle conversation with the terrorist, instructs the Vice-President to.
 * In John Sayles's Matewan, Danny (a teenager active in union organizing) is doing some lay preaching in the local church. He knows that the coal company has The company-enforcer thugs have told Danny not to say anything about the plot, or political at all, while he's preaching. So he tells the congregation the story of how Potiphar's wife tried to seduce Joseph and failed, and she tried to frame him out of jealousy, to get his point across.

Literature

 * How I Survived My Summer Vacation by Bruce Coville has a rather puckish ghost that only the protagonist can see, who at one point congratulates the protagonist on being able to do this.
 * In "The Borders of Infinity" by Lois McMaster Bujold, some of Miles' more oblique comments to his fellow prisoners are really instructions to his Dendarii Mercenaries, who he knows are listening in, telling them that he's changing the plan in mid stream. The reader is kept in the dark about that until late in the story.
 * Star Wars Expanded Universe:
 * In the Hand of Thrawn duology, the Con Man Flim, impersonating Grand Admiral Thrawn, tries to talk down a pirate ally who wants to kill one of Flim's allies. He suggests a new alliance. A Mistryl shadow warrior with a grudge against the pirate is eavesdropping, having taken out the pirate's backup, and when the pirate decides to ignore the offer she kills him. In the ensuing conversation, Flim tells the shadow warrior that he knows what she is, knew that she was there, and his offer was actually for her. Later he admits to his allies that he hadn't known any of that; when she'd appeared he'd just recognized that she was a Mistryl shadow warrior. He's just very good at rolling with the punches.
 * Thrawn himself pulls off a multitasked conversation in Side Trip, a collaborative Michael Stackpole / Timothy Zahn novella in Tales From The Empire. Disguised as a helmeted bounty hunter, he gets Corran Horn to go along with him into a criminal's fortress, then turns a blaster on him and helps the criminals stick Corran in the jail. While Corran blusters and threatens retribution, Thrawn tells him that he looks forward to when Corran gets out, since he's the only one standing between Corran and freedom. Come find him. To the criminals, and admittedly to Corran, this is a threat. To himself and Corran's more rationally-thinking father, who he's come to save, it's an announcement that this is a Trojan Prisoner scheme, since Thrawn provided a way for them to break out.
 * Happens in Discworld's stand-alone novel Small Gods. The central premise is that gods need belief to exist, and the book's God, Om, has only one believer left. He and said believer, Brutha, travel together, but since nobody else believes, nobody else can hear Om's voice. This leads to some interesting situations where Brutha and Om are trying to yell at each other (usually about some demonstration of godly powers or the lack thereof). It doesn't help that Brutha Can Not Tell a Lie, although over the course of the book he does get better at twisting the truth.

Live Action TV
"'''Hardison": Excuse me for interrupting Prom Night with my annoying felony burglary."
 * This happens a fair amount in Slings and Arrows, with Geoffrey talking to his Spirit Advisor Oliver. He doesn't seem to worry much about being comprehensible to anyone else, but he often is anyway (if not necessarily politic--at one point he screams "For the love of God, will you please shut up!?" at Oliver in the middle of a rehearsal).
 * Jack pulls this off handily in an episode of 30 Rock, talking to a client on the phone while answering Liz's questions in person.
 * This happens a lot in Leverage. The team's ubiquitous use of earbuds and cellphones makes it happen very naturally.
 * In "The Bank Shot Job", Nate finds himself trapped in a bank that's being robbed while using an earpiece to communicate with the rest of his team. He manages to cloak everything he says to them under the guise of a conversation he's having with the corrupt judge who's right next to him. Eliot, by contrast, simply walks to the other side of the police line after they've set it up and stares intently at the bank, having a conversation with Nate without even bothering to have a cover story. When a policeman tries to tell him that he needs to be on the other side of the tape, Eliot turns and growls, "I wasn't talking to you."
 * In the later episode "The Fairy Godparents Job", Parker talks Hardison through deactivating a security system through her earpiece while talking to the FBI agent that is infatuated with her at the same time. This was also while Hardison and Parker were playing the role of undercover FBI agents.

"Baltar: (Speaking to both Six and President Roslin) And I'm not your plaything!
 * And in another episode, The Boys' Night Out Job, Nate talks to Elliot and Hardison on a cell phone, while at the podium at an Alcoholic's Anonymous meeting, in front of a crowd of other people who think he's talking to his ex-wife.
 * In season one of Roswell, Michael needs Maria's car to get to a big geodesic dome, while she needs to interview him for English. Things go a bit wrong, he ends up driving her there against her will, and she manages to surreptitiously call Liz on her cell phone and have a conversation like this (saying things along the lines of "Boy, Michael, it's really strange to be alone with you... in my car... going to the dome...").
 * Gaius Baltar tends to do the fortuitous version with Head!Six on Battlestar Galactica Reimagined, with the twist that it's often difficult to believe that nobody notices something's going on.

Six, Roslin: Plaything?

Baltar: Yes, and I don't need to take this from either of you. (Realizes that Roslin can't see Six. Points at her aide, sitting in the corner.) You, or you!"

"Spike: Everyone's talking to me. No one's talking to each other."
 * Oh, they notice. They just assume he's crazy, and y'know... he is. So.
 * In Quantum Leap Sam tries to talk to his Invisible to Normals Ninja Butterfly Al in private as much as possible, but he's had to do this a few times.
 * Happens a lot in Randall and Hopkirk Deceased, with Jeff talking to Marty.
 * Bones:
 * A run of the mill one happens when Brennan is talking to Sweets' girlfriend over problems in their relationship. Cam comes in with DNA evidence from a murder weapon where the gender was in question. Brennan says one word in response: "Sex?" ...needless to say, as Sweets' girlfriend didn't hear Cam come in, Hilarity Ensues.
 * It also happens frequently when someone is questioning a suspect in the interrogation room, and someone else is talking to the interrogator from behind the one-way glass. When this happens, the interrogator will usually respond to the person on the headphones, and the suspect will think they were talking to them.
 * Buffy the Vampire Slayer manages a double of these -- Spike talks intermittently with Buffy and Willow, but they can't hear each other and just assume he's even more insane (to be fair, he is insane at the time, but everything he says is at least a little relevant to the conversation). He also talks to somebody neither Buffy, Xander, or Willow can see or hear. After you've seen the entire season, it becomes obvious that he's talking to The First.

"Dead Bob: But that was good, though, measuring the Yank's...
 * Occurred several times in Being Human.
 * Coupling: Poor Jeffrey ends up stuck talking to his girlfriend on a mobile and another girl who fancies him simultaneously. Julia asks him if he loves her at the same moment as Wilma asks him if he fancies her. Jeff is forced to answer, "Yes," and spends the rest of the following episode trying to get rid of Wilma.
 * Happens on occasion in Due South, as Benton Fraser alternates between talking to the (invisible-to-others) ghost of his dead father and whoever else happens to be present at the time, usually one of the Rays. Notably, being Fraser, he manages to carry on two conversations at the same time while hardly missing a beat.

Fraser: Thank you.

Ray Kowalski: What for?

Fraser: For driving the car.

Ray: You're thanking me for driving the car?

Dead Bob: Of course, one Yank is pretty much like another, anyway.

Fraser: People are not interchangeable like snowmobile parts.

Ray: There you go with the obvious again.

Fraser: You're right about that. What I think we should do is... (etc.)"

"Frasier: To my brother... and the woman of his dreams."
 * Occurs in Frasier, albeit with a fairly complicated set-up. His newly-married brother, realizing he's in love with another woman, is being forced to maintain a sham relationship with his wife Mel in order for them to both maintain some dignity in the break-up - but she insists on dragging it out and humiliating him. At a party, Mel forces Frasier to give a speech honoring the marriage - and he manages to give a full-length speech worded vaguely enough that anyone knowing the full situation can tell it's a toast to Niles and Daphne instead. Mel isn't amused...

"O'Neill: (to Ballard) So, Daniel says you have to go with us, because you've been through this before and the aliens won't show up unless you're there.
 * Doctor Who:
 * "The Sontaran Stratagem / Poison Sky": The Doctor's nonsensical babble (well, it's not strictly out of character for him...) addressed to General Staal is actually a secret message to Donna.
 * He does the same thing in "The Age of Steel" to secretly give Mickey instructions in the middle of one of his "I've figured out exactly how to defeat you" speeches.
 * In one episode of Stargate SG 1, the Phlebotinum of the Week made Daniel Jackson "out of phase", and the only one who could see or hear him was his grandfather Dr. Nicholas Ballard, who was declared crazy when he tried to talk about his encounter with identical Phlebotinum on Earth. Communicating with his teammates through Ballard, Jackson managed to convince them to go back to the planet and let the Applied Phlebotinum finish what it was doing before it was interrupted.

Jackson: Hey, wait a minute, I never said that! Grandpa, you're taking advantage of me!

Ballard: Yes."


 * In a season five episode of House, a sleep-deprived Dr. House carries on conversations with a hallucinated vision of Amber Volakis, who died in the previous season. He knows she's not actually a ghost, but since she remembers things that he knows but thought he forgot, he uses her as a hotline to his subconscious. He eventually covers up talking to her in public by wearing a Bluetooth headset.
 * Walt does this basically any time Jesse calls him at home in Breaking Bad.

Machinima

 * In the fifth season of Red Vs Blue, before Sarge and Donut find Grif and Simmons, Sarge communicates with Simmons via their helmet radios. Donut's radio is broken, so he is completely unaware Sarge isn't talking to him.

Theater

 * Willy Loman from Death of a Salesman does this while talking to his neighbor Charley: he imagines that his dead brother Ben is present and gets confused trying to converse with them both at once.
 * In Blithe Spirit by Noel Coward, Charles talks several times to the ghost of his first wife, and his second wife thinks he's talking to her.

Video Games

 * One of the puzzles in Tales of Monkey Island: Rise of the Pirate God involves finding dialog lines that are simultaneously insulting to a challenger and consoling to a crestfallen ally.

Web Comics

 * Shows up in the webcomic Cardboard Angel here when Mayu tries to reprimand the ghostly, and only visible to her, Yuuji who was trying to invisibly mess with the guy she likes.
 * In this installment of The Last Days of Foxhound, Liquid pulls this off accidentally, giving responses to the ghost of Big Boss that coincidentally sound like responses to what Psycho Mantis is saying.
 * In Touhou Nekokayou, Sanae has a conversation which sounds like "I'm not treating you as a serious threat" to Meimu and a sort of in-character "Stop Helping Me!" to Suwako.

Web Original

 * Done by Twilight Sparkle in this My Little Pony: The Mentally Advanced Series
 * The Joker Blogs: While driving through a security checkpoint, Dr. Arkham tries to tip off the security guard that The Joker has taken him hostage and is hiding in the back of his car. Unfortunately for him, the guard doesn't pick up on it... But The Joker does.

Western Animation

 * In The Venture Brothers:
 * Doctor Orpheus uses Astral Projection to talk to his vampire hunter and alchemist buddies and gets the lines crossed.
 * Also happens when 21 has a conversation with the Monarch and
 * An episode of Batman: The Brave and the Bold cleverly played with this one. During an excursion to a parallel universe, Batman's partner of the week, Red Hood, is captured by the bad guys. As their leader, Cyclone, attempts to interrogate him, Batman (who is eavesdropping via comlink) is simultaneously sneaking through the building to rescue him; Red Hood phrases his responses as coded directions to lead Batman to his location. Although successful at first, the trick soon breaks down; Cyclone quickly detects the pattern in Red Hood's answers and realizes what he's doing. Fortunately, Batman has already arrived by then.
 * This trope is basically the entirety of Rummy's interactions with Ed III in the Boondocks episode "Thank You For Not Snitching", due to Ed III's affinity for his new Bluetooth earpiece.
 * In Generator Rex Cesar notices that someone cloaked is following him and the providence agents, since they plan on blowing up the area after they're done searching it, he loudly announces it for the sake of the cloaked followers