Sheldon: How will Raj ever reach true greatness if his friends lower the bar for him? When I was eleven, my sister bought our father a "world's greatest dad" coffee mug, and frankly the man coasted until the day he died.

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.

Howard: Sheldon, don't take this the wrong way, but, you're insane.
Leonard: That may well be, but the fact is it wouldn't kill us to meet some new people.
Sheldon: For the record, it could kill us to meet new people. They could be murderers or the carriers of unusual pathogens. And I'm not insane, my mother had me tested.

Leonard: [to a "smiling" Sheldon] We're here to see Koothrappali, not kill Batman.

(Sheldon smiles in a grotesque way).
Howard: Oh crap that's terrifying.