Dating Service Disaster

And while I don't know your real name, your real age, or your shoe size,
I will leave this bedroom chair and this keyboard behind

—Noah and the Whale, "Second Lover"

In Real Life, online dating sites are simply another way of meeting people. By posting information in their profiles about their interests, beliefs, and hobbies, a reader can make a rational decision about whether or not this person is worth getting to know, and can chat through email or instant messaging until both are comfortable enough to meet in the flesh...

...unless you happen to be a character in a Sitcom, in which case the online dating service is yet another tool the writers will employ to turn your life into a swirling miasma of entertaining chaos. If you use a dating service, you can expect the first person you'll be matched up with to be:

Your most hated enemy.
A gorgeous woman who seems strangely familiar to you. At the end of the date, you'll discover that she was actually the captain of the football team at your old high school and that something's different about her now.
A doughy and unattractive loser whom you'll discover to be either very, very nice or very, very rich, thus teaching you a valuable Aesop (probably a Family Unfriendly one in the latter case) about how not to judge people by their initial appearance.
The Grim Reaper, who's actually kind of shy and nervous about this whole "online dating" thing. He hopes you don't mind if he takes his scythe and his cell phone along; he kind of needs them for his job.
A serial killer.
An inhuman monster
One of your relatives.
Your Psycho Ex.
Your best platonic friend. Kiss that excuse good-bye.
Your current boyfriend/girlfriend, who you hoped wasn't going to find out about this (though they can't exactly complain themselves).
A con artist.
Advance-fee fraudster (very much Truth in Television)

There are many other permutations and possibilities available, but no matter whom your suitor might turn out to be, the odds are very high that your first date will be anything but typical. If you're using an international dating or marriage agency, then expect an even bigger minefield, sometimes with a Family-Unfriendly Aesop about how we should stick to our own kind.

If you meet a love interest over the internet by chance rather than through a dating agency, the results will be similar. Especially if the producers want to drop the New Media Are Evil anvil. It can also be a case of Did Not Do the Research, as online dating sites tend to work a bit differently than the dating services of old. For one thing, most dating sites let users post pictures of themselves in their profiles. This alone would prevent half of the scenarios above, and users are always advised to avoid those who don't have photos. Fiction might get around this by making the prospective date's photo extremely misleading (eg, the infamous "Myspace Fat Girl Angle").

Older Than They Think, with pre-Internet "computer dating" and "video dating" services providing examples for this trope. However, online dating as a source of humor/drama is not used very much anymore, with the internet becoming more mainstream since the early 2000's and the stigma attached to online dating not as strong as before (especially among gays and lesbians whose dating options are fewer and harder to find if one doesn't like bars). The Blind Date trope is as strong as ever, though, and fulfills the same purpose as this.

See also Mailer Daemon if the love interest turns out to be the matchmaking computer itself. For a similar service but with face-to-face interaction, try Speed Dating. For a more general discussion of dating disasters, see Bad Date.

Examples of Dating Service Disaster include:

Advertising

The London Review of Books has a personals column full of intentionally unattractive ads like "Some chances are once in a lifetime. Not this one, I've been in the last 12 issues." or "Tap-dancing Classics lecturer. Chilling isn't it? (M, 38)" One hopes this is a subversion and the actual advertisers are better than their description.

Comics

In Marvel Adventures: Avengers Hawkeye signs on to a dating service online, but finds filling out all the personal info too much work, so he decides to upload his personal info from the Avengers' database instead. However, he succeeds in uploading everyone's personal info, and the Avengers are swamped with people who claim to have dates with them. The owner is an ex-supervillain (Batroc) who delightfully refuses to take down the info unless they comply, since it is good PR for his site to have celebrities using it. Hilarity Ensues.

Film

The movie Must Love Dogs is a romantic comedy about a couple who meet via online dating. True to form, the main heroine arranges a date with a suitor who turns out to be her own father.
The movie Napoleon Dynamite has the dorky, nebbish Kip hitting the jackpot when the girl he's been chatting with online turns out to be Lafawnduh, a gorgeous African-American woman with a fun personality. Lafawnduh thinks she struck gold, too.
Exploited by the movie Sneakers. To infiltrate a secure facility, the team finds an employee who's been looking for love online and sends the protagonist's ex-girlfriend to go on a date with him so she can steal his ID card and record a voice sample to access the guy's room. He gets suspicious, takes her to his office and alerts the villain. She tries to talk her way out of it and seems to have succeeded. As the villain walks away, she humphs that this is the last computer date she's ever going on. At which point he stops, turns round and says, "A computer matched her with him? I don't think so..." and knows something's up...
Pretty much the whole PLOT of You've Got Mail - they turn out to be (mutually hating) business rivals in real life. The situation is exacerbated when he finds out... but she doesn't.
- You've Got Mail is based on the much older film "The Shop Around the Corner", which was released in 1940, in which two anonymous pen pals fall in love with each other without realizing that they hate each other in real life.
Another Older Than They Think example: Multiple variants of the trope in Carry On Loving (1970) -- although the "computer" in this case is a very impressive wall of tape reels and blinking lights ... behind which is the manager's wife with a card index. The main plot is that she intentionally sets up the first hapless customer with her husband's girlfriend.

Literature

In A Dirty Job, one character is prone to online-dating girls from Southeast Asia, who invariably turn out to be sixty years old or actually men or otherwise not what they claimed to be.

Live Action TV

The Odd Couple: before the internet—before PC's even—there was computer dating, believe it or not. In a episode which aired circa 1971, Oscar signs up with a computer dating service and embellishes his bio. He winds up matched with Felix's ex-wife.
The Fresh Prince of Bel-Air: Brother and sister Hilary and Carlton get matched up.
iCarly: Spencer, using whynotdateme.com
The Drew Carey Show: Drew meets a woman online and engages with cybersex with her, only to discover later it's his archnemesis, Mimi. In a very odd Crowning Moment of Heartwarming, Drew comforts Mimi (in real life) after her mysterious beau ditches her and disappears.
On Parks and Recreation, Leslie Knope is horrified when a matchmaker site pairs her with her horndog coworker Tom. (Turns out, Tom had set up 26 different profiles to match himself with every possible female personality type.)
In the 1992 series Down The Shore, overweight, nerdy Eddie meets a girl online, but chickens out at the last moment and has handsome-but-dumb housemate Aldo pretend to be him for their first in-person meeting. She turns out to be a knockout (played by Kathy Ireland) who was tired of shallow guys hitting on her for her looks and who was looking for an intelligent man attracted to her mind; she quickly sees through the switch and happily meets the real Eddie.
Raven and Eddie are matched up on That's So Raven.
A variation happens on Friends to Chandler on at least two occasions (once it was a blind date, the other time they met online), both times with his ex-girlfriend Janice.
How I Met Your Mother used this trope twice (possibly three times) with Ted. The first time Ted went to a matchmaking agency with a 100% success rate, but it turns out they literally have no women compatible with Ted. The second time the same agency gets back to him with a perfect match, but he passes up the date for another shot at the Will They or Won't They? relationship with Robin. The third time Ted meets a woman online who turns out so far into the crazy end of the Hot-Crazy Scale; in a twist at the end it's revealed that she and Ted "met online" while playing World of Warcraft.
Used in the Season 3 finale of The Big Bang Theory. And subverted. Howard and Raj sign Sheldon up for one as a joke, but the site gives them a match. Sheldon, thinking the entire thing was stupid when they finally tell him, only goes on the date to prove that dating sites don't work. Ironically, Sheldon's match happens to be perfect—a female version of himself. Apparently, she only used the site because she promised her mother she'd date at least once a year.
- Sheldon also creates a fake dating profile for Penny in hopes that she'll find a boyfriend and stop pestering him for video gaming advice.
In the Three's Company episode "Mate For Each Other," roommates Jack and Janet each secretly try out a "computer dating" service, only to end up matched with each other.
Happens on the UK version of The Office, when David Brent uses one in the 2nd Christmas Special. Michael uses a more traditional method in the US version: bullying his subordinates to offer up names of eligible friends.
A victim of the week in Bones was using a cell phone dating service that Hodgins was also using. Angela later started using it and they popped up on each other's phones later.
Bosom Buddies had a "video dating" example, where a woman seems to be a perfect match for Henry until they meet face to face, and he discovers that, among other things, she's really into Satanism. (Of course, it's also possible that she wouldn't be crazy about Henry's own secret.)
The X-Files has the episode 2Shy, in which a serial killer is finding his victims/food via dating sites.
In the episode of The Nanny called "The Fifth Wheel", C.C. (who goes by "goodnplenty") gives up men after finding out that "porchepuppy" was actually 15-year-old Brighton. She is surprised by his vocabulary.
3rd Rock from the Sun did this with newspaper personals. While Dick and Mary were on the outs, Dick placed an anonymous personal ad in the paper. Someone answered it and asked to meet him at a restaurant. It turned out to be Mary, of course, and they immediately decided to Never Speak of This Again.

Music

Musical example: Rupert Holmes' infamous Escape (The Pina Colada Song) is about a pair of bored lovers who secretly arrange to date other people via newspaper ads; to their surprise, they discover that they're cheating on each other with each other. The various violations of conventional morality, not to mention simple logic, implied in this song were heavily deconstructed in a particularly memorable sketch on Mystery Science Theater 3000.
Noah and the Whale's "Second Lover", whence the page quote, is about an online affair.

Newspaper Comics

Happens in early Dilbert before it went to solely office-comedy.
In 2009 Mary Worth featured a character named Ted Confey who was dating Dr. Adrian Cory after meeting her online. He proceeds to bilk her out of $50,000 using lines a three-year-old would see through. Just as he's ready to disappear, he's arrested by a Santa Royale detective who later asks Adrian out - and who turns out to be the son of Adrian's father's old college roommate (whom he seems to have cared about a great deal...). The moral of the story? Finding partners in new ways bad, going out with someone approved of by Dad good.

Theater

One Christmas panto version of Beauty and The Beast has the Beast's servants try creating a profile for him on such a website so that he can find his true love and break the spell—although they keep putting things they like on the profile rather than things the Beast likes. This plan is discarded once Beauty shows up, of course.

Video Games

Miranda in Mass Effect spends some time on online dating sites. She doesn't have much luck.
- This isn't a true example of this trope, however, since she appears to only be reviewing (and rejecting) potential matches on the site without meeting any of them.
Sybil in Sam and Max once runs a computer dating service. Her computer matches Sam and Max to each other—perhaps because they are the only entries in the database.

Webcomics

For a time, webcomic Least I Could Do advertised its own dating service with the line "Meet the 40-year-old trucker of your dreams!"
In the Insecticomics, Bombshell sets up 'Dr. Shell's Love Connection", mostly for kicks. He hooks up Vector Prime with Hotshot (who Vector Prime hates)...and Vector Prime later goes on about how wonderful the evening was. He's lying, though.
In Ctrl+Alt+Del, Lucas tries to use this, but he is repelled by the first photograph he sees (saying that it's hard not to judge a book from the cover when it's made of fur). Then, Zeke decides to play a practical joke on Lucas and sets him on a date with a girl that is slightly fat... but, in the end, she turns out to be a beautiful girl (she was wearing a fat-suit).

Western Animation

In an early episode of Johnny Bravo, Johnny arranges a date with a woman he met online... who turns out to be a talking antelope named Carol.
Totally Spies!: The villain-of-the-week starts a phony digital dating service and sets himself up (in a variety of disguises) with every girl at Beverly Hill High so he can dump them and break their hearts like his ex did to him. Yes, it's an incredibly lame plot.
The Boondocks episode "Attack of the Killer Kung-Fu Wolf Bitch" (yes) has Granddad trying to date over Myspace. The first several women he meets are grotesquely ugly and lied about their appearances; he finally meets the titular character, an attractive, cheerful woman named Luna (voiced by Aisha Tyler) who just happens to a psychopathic kung-fu master who was raised by wolves.
In the Futurama episode "Put Your Head On My Shoulders", Bender runs such a service, which is both discreet and discrete.
Happens in the Code Lyoko episode "Deja Vu", where Odd arranges a date with a girl he met on an online dating site. Said girl turned out to be Sissi of all people.