Camping a Crapper

Jeff: You planning to win the whole game camped on a crapper?

Britta: Worked on you, didn't it?

—Community

When you gotta go, you gotta go, and everybody's gotta go sometime, so what better time to make someone take their final exit than waiting for them to evacuate?

What's that? Needlessly cryptic? Fine. Let me spell it out: If you want to kill somebody, wait until they go to the bathroom.

If the toilet is used for the kill, then The Can Kicked Him, if not, then Swirlie.

As a Death Trope, Spoilers ahead may be unmarked. Beware.

Examples of Camping a Crapper include:

Anime and Manga

Panty & Stocking with Garterbelt: Panty tries this against Stocking (who responds by wearing diapers) when they were conducting full scale warfare while transformed into alien robots.
In the Monzetsu hentai series, this is one of the most common places for "trysts" (read: rapes) to occur.

Comic Books

Mentioned by Spider Jerusalem in Transmetropolitan when he's attacked by two assassins. To paraphrase: "You can't even come up with a good murder plan. I consume drugs in every form 24/7 and spend four hours a day on the crapper! Murder me then!" and one of the assassins agrees with him, saying: "Bob, this really was a crappy plan."

Film

Julian's favorite theory of assassination in The Matador.
- Referred to by the lead as the 'Gotta Pee Theory'.
In Unforgiven, Quick Mike, one of the two cowboys the protagonists are after, is being guarded inside a house. They wait until he leaves to use the outhouse to kill him.
Austin Powers International Man of Mystery. The Irish assassin Patty O'Brien waits until Austin is in a public restroom stall to try to kill him.
- And in the sequel, Scott suggests that instead of going back in time to steal Austin's mojo, they should just go back and shoot him while he's sitting on the crapper.
In The Pink Panther Strikes Again, two assassins get into bathroom stalls on either side of Clouseau's stall. He drops the toilet paper, reaches down to get it, and the assassins shoot each other.
In Zombieland, one of Columbus's rules was "Avoid Bathrooms". Because if anyone ever got zombified in a bathroom, they'd pretty much just be stood there till someone came in and dropped their pants, making an easy target.
Omar Epps gets stabbed in the head through a bathroom stall early on in Scream 2.
Averted in Leon the Professional. Little Miss Badass Mathilda tries to ambush Dirty Cop Stansfield in the DEA restroom. Unfortunately Stansfield is hiding behind the door, not sitting in one of the booths.
In the first Bad Boys movie one of the protagonists is fighting desperately with a mook in the male toilets while his partner is blissfully enjoying the go-go dancers outside.
Averted in Halloween: H20. A woman and her daughter go to a public bathroom and Michael Myers follows them in. After a tense scene in which the audience assumes he is going to kill them, he ends up stealing the woman's car keys instead.
A nonfatal example happens in Three Ninjas. One of the boys tricks one of the kidnappers into drinking a milkshake filled with laxatives. When the guy rushes to go use the bathroom, the kid pops back in and beats him with a toilet plunger.
How The Bride captured O-Ren's secretary.
In Snakes on a Plane, three different people get attacked in the airline's lavatory by the eponymous snakes: a man on the toilet who receives a Groin Attack, and a young couple who suffers Death by Sex.
A Spaghetti Western had a killer move the outhouse back a few feet, so that when the target went out for a late night constitutional, he fell in the pit and was shot while standing waist deep.
The first of the hapless vacationers to be killed in the Scandinavian Nazi zombie flick Dead Snow is in the cabin's outhouse when it happens. Though if memory serves she'd gone there for a quickie instead of the usual business.

Literature

The whole murder plan of Dead Famous by Ben Elton hinged around this. Geraldine the producer realised that at least one girl would leave the cabin to go to the bathroom, allowing her to be murdered.
Tyrion Lannister does this to his father Tywin in A Song of Ice and Fire.
Book of Judges - one of the judges assassinated a king while he was on the can. The assassin slipped out because the guards assumed the king was taking a really long dump and didn't want to intrude.
- Averted later. King Saul chases David, enters a cave - alone, where David happens to be hiding. However, while Saul is... distracted, David only uses the opportunity to cut off a piece of his clothes.
In The Sword of Truth, a general tells he once crushed a rebellion with vastly inferior forces - using the fact that most of the rebels were literally with their pants down.
In Robert Aspirin's Myth Adventures series, Skeeve's various bodyguards have made it a point to state that people have often been killed going to the can or on the can. Thus they always precede him into and out of the can, and only leave him alone there if they're very confident.
Terry Pratchett mentioned this in one of the Discworld Witch books, set in Lancre. Sometimes the royal succession has been hastened thanks to a very determined assassin crawling up the privy. Which is at the top of a tower. Most likely inspired by assassination of Uesugi Kenshin.
Subverted in Battle Royale, when Sho Tsukioka attempts to ambush Kazuo Kiriyama coming out of the toilet where he can be heard taking a leak. The clever Kiriyama, however, has rigged up a water bottle to simulate the sound of urination, and Tsukioka meets his end as the zone becomes a forbidden area, and his collar detonates.

Live-Action TV

The Trope Namer is Jeff's analysis of the girls' strategy in the Community episode "Modern Warfare".
- And in season two's paintball episode, Pierce becomes something of a Cattle Baron when he hides in a bathroom, and discovers people are willing to exchange their ammunition to use the facilities.
In The Goodies episode "Daylight Robbery on the Orient Express", the Shafts are killed when the lavatory on the train blows up while they using it.
As a T-1000-like Terminator in The Sarah Connor Chronicles, Shirley Manson disguises herself as a urinal, then kills the man who moments earlier was urinating into her, with an unfortunate attempted Bond One-Liner: "You really piss me off."
On Boardwalk Empire Owen Sleater waits till his target goes to the bathroom before following the man into the bathroom and killing him with a garrote.
Pointed out in Burn Notice season 4 when they kidnapped a mobster while he was about to use the can.
A plan suggested but not executed by the guys during a Big Bang Theory paintball game.

Newspaper Comics

There's a The Far Side cartoon depicting a hunter near a toilet with a picture of a deer on it, with the caption, "He only had to wait. The deer would come. The deer would come."

Live-Action RPG

In Real Life games of "Assassin" and "Humans vs. Zombies" (essentially glorified games of tag with Nerf guns), this is also a very useful tactic. Although most sets of rules designate the bathroom itself as a safe zone, it's easy to ambush someone entering or exiting.
- It had to be modified to make the bathroom a safe zone after people abused the rules making nudity itself the safe zone. By running around naked.
According to Harpo Marx's autobiography he was in a game of "Murder" - where the assassin tells the victim "you are dead" and they must fall down dead at that spot - and he wrote "you are dead" on a sheet of toilet paper, so the person was trapped there until somebody else had to use that particular bathroom. But once the body was found it was easy to find the killer because Harpo (who had less than a full 2nd grade education) had written "you are ded."

Video Games

This is one of the ways you can ambush other players in the Source Game Mod The Ship.
A VERY good tactic in Hitman games, both for knocking people out and outright killing them.
A lot of multi-player FPS games, especially the ones based in smaller locations like Counter-Strike and such, you can often surprise someone doing this.
An attempt at this is made on Travis at the end of No More Heroes. Luckily, Henry saves him. Supposedly this is why in the sequel, he keeps his various beam katanas at the ready on his belt.
On the multiplayer level 'Facility' of GoldenEye, upstairs bathrooms were easy turn into kill zones by campers.
- Especially since the most powerful weapons spawn in there (if you don't move around too much), i.e. Magnum, Golden Gun, etc.

Web Comics

Ctrl+Alt+Del: During the Game Games Bowl short story, Ethan is wary about using the port-a-potty in case someone is trying this. His fears are unfounded. However, the toilet is booby trapped as part of the game.
In Schlock Mercenary, while reconquering the team's ship, Schlock ambushed one of the boarders by shapeshifting into a toilet seat. This obviously wasn't a perfect plan. But it worked.

Web Original

The Onion: "Osama bin Laden killed while sitting on the toilet, Nation likes to imagine"

Real Life

As far as it's known, Ukifune Jinnai, a ninja of Sengoku period in employ of Oda Nobunaga, assassinated Uesugi Kenshin using a spear from ambush in the latrine chute. For most people a chute would be too small, but he was a dwarf and specifically trained for this job. Also, the Daimyo in question had very tight security - including ninjas, who wiped out the first team from Jinnai's clan, so there was a matter of restoring the clan' honour after a big failure, too.