My Sister Is Off-Limits/Quotes

Everything About Fiction You Never Wanted to Know.

"She's Ron's sister, Harry told himself firmly. Ron's sister. She's out of bounds. He would not risk his friendship with Ron for anything."
Harry Potter, who, of course, ends up married to her anyway.

"You wanna fuck my sister?"
"You wanna fuck my sister!?"

Stephen Lynch, The Best Friends Song
If your sister hangs around your friends, eventually one of them is going to hook up with her.
From a Spike TV commercial describing lessons learned from Star Wars

Private Joker: "I wanna put my tubesteak into your sister. What'll you take in trade?"

Private Cowboy: "What've you got?"

Trunks: "Goten's not your type."
Bra: "So what is my type? Since you seem to know what I prefer."
Trunks: "Someone who isn't Goten."

"What a girl! I think she likes you. Word to the wise, though - she don't put out. Which is convenient, 'cause if she did, I'd have to kill you."
Patrick "Packie" McReary telling the protagonist about his sister, Kate.

(401:) Dude. My sister is off limits. Touch her again and I'll rip off your dick and force feed it to you.

(301:) I accept this challenge.
Texts From Last Night
(336:) If I die tonight, I want you to know that your sister is awesome in bed.
Texts From Last Night

(813:) I'm fucking your sister right now.
(1-813:) You motherfucker.

(813:) She's next.
TFLN likes this trope. This isn't even close to all of them