Leslie: So, dumbass, I heard you made a grad student throw up last night.
Sheldon: The truth can indeed be a finger down the throat of those unprepared to hear it. But why should I cater to second-rate minds?
Leslie: Because first-rate minds call you "dumbass"?

Leslie: There's no reason to feel uncomfortable just because we've seen each other's faces and naked bodies contorted in the sweet agony of coitus. Rest assured that any aspects of our sexual relationship regarding your preferences, your idiosyncrasies, your performance, are still protected by the inherent confidentiality of the bedroom.

Leslie: Hello men. Sheldon.

Leslie Winkle: Uh, in the past, I would've said something obnoxious, like, "Happy birthday, dumbass". But I'm not gonna do it. You and I have both grown a lot, and it's just so nice to see you all again. So happy birthday, Sheldon.
Sheldon: Oh. Oh, now, you know I hate change. Say it.
Leslie Winkle: Happy birthday, dumbass!

Raj: Isn't there a policy against dating graduate students?
Leonard: No, if you can talk to them, you can ask them out.
Raj: Damn, there's always a catch.

Penny: Whats Sheldon's deal? Is it girls, guys, sock puppets?
Howard: We operate on the assumption that Sheldon has no deal. Though we have many theories about how he might reproduce. I'm an advocate of mitosis.
Penny: What?
Howard: I believe that one day Sheldon will eat an enormous amount of Thai food and spilt into two Sheldons.

Penny: Holy crap on a cracker!