Single-Malt Vision

"Billy Clanton: Why, it's the drunk piano player. You're so drunk, you can't hit nothin'. In fact, you're probably seeing double.

Doc Holliday: [takes out a second gun] I have two guns, one for each of ya."

- Tombstone

""Well, lookee here, two sets a' twins!""

- Town Drunk from Fable II

Booze makes you see double (or triple, quadruple, or more, especially if Rule of Funny is in effect), and sometimes the drunk will assume both of whatever he's looking at are real.

A variant has the drunk afflicted with double-vision trying to interact with "the one in the middle" (although since most people only have two eyes, normally you'd only see two of whatever it is).

Generally a Discredited Trope nowadays.

For hallucinating things that actually aren't there while under the influence, see Pink Elephants.

Comic Books
"Roman Legionnare: Come on, you two fattiesh! Let'sh fight! Obelix: (Offhand Backhand) There are not two fatties! There's only one, and he isn't fat!"
 * Rene Goscinny liked using this joke, especially when he was writing Lucky Luke or Asterix.

Film
"Terri: *giggles* I'm not gonna say anything. Well, maybe one or two things. C'mere. All six of you, come here!"
 * In the film It's a Wonderful Life, when a very humorously drunk Uncle Billy asks George Bailey which hat he should take, George says "the one in the middle."
 * In the early rounds of the Rocky vs. Drago fight in Rocky IV, Rocky remarks during a rest period that he sees three Dragos when he's fighting (although he's not drunk, but punch-drunk) and is advised by Paulie to "hit the one in the middle".
 * A similar sentiment was expressed by NFL player Kyle Turley after returning to the field with a concussion.
 * In Tombstone, Doc Holiday says he has two guns, one for each of the outlaw he needs to shoot.
 * Near the climax of Jumpin Jack Flash, Terri staggers back in to her job at the bank, having recently been drugged by one of the bad guys. Her boss informs her that she has managed to "shatter the Guinness record for tardiness", to which she replies...

Live Action TV

 * Father Ted: When Father Jack sobers up for the first time in years in "Cigarettes, Alcohol and Rollerblading", he looks up at Ted and Dougal and asks "Where are the other two?"

Literature

 * A Tourist's Guide To Lancre, in its description of a pleasant walk through the Lancre fells, advises those who started with a drop of scumble at the Goat & Bush to take the middle path.
 * In Life The Universe And Everything, a very drunk Zaphod is amazed to see Trillian sit on her own lap, before banging his heads together trying to get all four (justified: four eyes = four images) of her to resolve into one image.

Tabletop Games

 * A variation on this is described as a story in one of the old Dark Sun setting books. In it a half-giant is persuaded to drink less alcohol in a night, but gets in trouble on his first night doing so. The reason being that when he was more drunk and heading home, he always knew to take the middle road of the three he saw. After drinking less, he only saw two and didn't know which was correct. Which eventually gets him poisoned and robbed by a passing Elf.

Web Comics
"Gil: ...and how are you, mister Higgs? Higgs: (with lots of damaged plaster behind him) I'm... I'm good, sir. Lemme... at 'im... Lemme at both of 'im..."
 * Bob and George: George thinks he gets the same effect from dizziness; then, he admits his imprisonment has driven him insane.
 * Girl Genius, after Vole gone berserk and Higgs "kept him busy":

Western Animation

 * A slight variation on the trope (in this case, it's a played-straight version of the trope Concussions Get You High), in one episode of Looney Tunes Pepe Le Pew is struck on the head with a club several times by the cat he is always pursuing, causing him to see six of her. He replies afterwards, "The one in the middle may remain; the rest of you, another day."
 * The Simpsons has: "I'm seeing double... four Krustys!" A subversion, actually, since there really are two Krustys being doubled, and the mobster who said this wasn't drunk; he was rubbing his eyes in disbelief.
 * Daria: On the season two episode "The Daria Hunter," Jake and Mr DeMartino are getting drunk on whiskey and talking about their messed-up childhoods. When Helen comes in and shrieks that Jake is drunk, Jake laughs that he's not, followed by a cut to his POV where there are two blurry visions of Helen.

Real Life

 * From an Emo Phillips standup routine: "She sends me to the principal, and I get to his office and I sit down and he looks at me and says, 'Emo, Emo, Emo.' I said, 'I'm the one in the middle, you drunken slob.'"
 * This is the basis for the alleged "two hats" cure for the flu: put a hat on your nightstand, go to bed with a bottle of scotch, and keep drinking it until there are two hats on your nightstand.