Penny: What would you recommend as a present for a 13-year-old boy?
Stuart: A 13-year-old girl.

Stuart: Oh, Sheldon, I'm afraid you couldn't be more wrong.
Sheldon: More wrong? Wrong is an absolute state and not subject to gradation.
Stuart: Of course it is. It's a little wrong to say a tomato is a vegetable, it's very wrong to say it's a suspension bridge.

Leonard: Oh, hey, Stuart. This is Penny. She's looking for some comic books.
Stuart: Oh, really? Blink twice if you're here against your will.

Sheldon: You don't see it, do you? We're losing her.
Leonard: Okay, I'm going to make this very simple for you. You are not in this relationship, I am. Ergo, you have no say in anything that happens between me and Stephanie.
Sheldon: I'm afraid I can't allow that. Pursuant to Starfleet General Order 104 Section A, you are deemed unfit and I hereby relieve you of your command.
Leonard: General Order 104, Section A does not apply in this situation.
Sheldon: Give me one good reason why not.
Leonard: Because this is not Star Trek.