Leonard: Oh, Dr. Siebert, twelve o'clock.
Howard: Why's the president of the university slumming in the cafeteria?
Sheldon: Perhaps he's emulating Shakespeare's Henry V, who dressed as a commoner and mingled among them, to find out how he was being perceived by his subjects. Course, if he'd have read any of the thirteen hundred e-mails I've sent him on the subject of his administration, he could have saved himself the trouble.

Raj: I don't like bugs, okay. They freak me out.
Sheldon: Interesting. You're afraid of insects and women. Ladybugs must render you catatonic.

Sheldon: Scissors cuts paper, paper covers rock, rock crushes lizard, lizard poisons Spock, Spock smashes scissors, scissors decapitates lizard, lizard eats paper, paper disproves Spock, Spock vaporizes rock, and as it always has, rock crushes scissors.

Sheldon: Why are you crying?
Penny: Because I'm stupid.
Sheldon: That's no reason to cry. One cries because one is sad. For example, I cry because others are stupid, and that makes me sad.

Penny: Good morning, slut!
Leonard: What?
Penny: Oh, please! I recognise the walk of shame when I see it. All you're missing is a little smeared mascara and a purse with panties wadded up in it!

Sheldon: Given how much time you spend engaging in pointless self-abuse, you might consider, just this once, using your genitalia to actually accomplish something.

Sheldon: An entire dinner to talk about your research? Where you going? The drive thru at Jack In The Box?