A man, his wife, and his buddy are at a bar. After a few hours of heavy drinking, the wife says she's had enough and she's going out to sleep it off in the car.
Ten minutes or so later the buddy says he's going out to check on her. Several beers later, the bartender suggests that the husband go check on 'em both.
The husband stumbles out the door and sees his buddy and wife engaged in a few extracurricular dealings, then walks back in. He laughs and tells the bartender,
"That buddy of mine is so drunk, he thinks he's me!"