An "I know this guy" story is a bullshit story where one person thinks up something funny, cool, gross, weird, or sexy, but essentially untrue, and tries to pass it off as true by framing it as if it happened to someone they supposedly know. It's similar to the "I have this friend" story, where someone asks for advice about a problem that's really about them but they're too embarrassed to say so. "I know this guy" stories are purely about entertainment, however, not about seeking advice.
Jerry: "I know this guy... he caught his sister having sex with their cousin and two friends in their uncle's bed."
Joe: "Sure, Jerry. You *know* this guy. Riiight."
Jerry: "I swear! It's true!"
Joe: "Bullshit. What was the guy's name then?"
Jerry: "Well I don't *know* him, but I heard about it."
Joe: "Sure you did. Sick pervert."
Joe: "Sure, Jerry. You *know* this guy. Riiight."
Jerry: "I swear! It's true!"
Joe: "Bullshit. What was the guy's name then?"
Jerry: "Well I don't *know* him, but I heard about it."
Joe: "Sure you did. Sick pervert."
by kevnar February 19, 2007

A response to urges to do better academically, though it is not limited to school. It is commonly used to show indifference to a suggestion.
by dacousin January 5, 2011

Alex: Someone made a rumor about you.
Amber: I ain't on that shit!
Whitney: But I wanna go to the mall!
Crystal: I ain't on that shit!
Amber: I ain't on that shit!
Whitney: But I wanna go to the mall!
Crystal: I ain't on that shit!
by Amber Walker September 10, 2006

K- "Maddi, I wuv oo more than owls!"
M- "ohhhh, that's the most undying statement of love I've ever heard. I wuv oo too!"
M- "ohhhh, that's the most undying statement of love I've ever heard. I wuv oo too!"
by SecretSquirrelBusiness September 6, 2010

"More," Britney replied.
by Hampikizzel Fo' Shizzel June 2, 2005

For Example, Mick says I want to go to the bar, I want to go to the bar to drink, Mack says no mate I don't want to be responsible for you. Mick says OK, I'm leaving you here, I don't care. Mack says don't be like that you don't understand and tries to explain the situation and wishes the topic never came up. Mack lectures Mick and tries to stop Mack going into the bar knowing he will get drunk but also not wanting to leave his friend. Mick is insistent gets drunks gets arrested or ends up vomiting and the next day blames everything on his good friend Mack. Mack says I see how it is
by DaffyDucks August 22, 2012

aron is the fattest ugly stupid motherfucker ive ever seen in my life. when I glanced at him the first time I almost shit my pants from how fat and ugly and a stupid nigg- he is just so motherfucking stupid I want to die
by aaaaaaaaaaaaaaaaaaaaaaaamen September 20, 2019
