Sheldon: I'm the guy.
Penny: You're not the guy.
Sheldon: Are you sure? It would explain so much. Your constant presence in my apartment. That baffling dalliance with Leonard just to be near me. The way you call me sweetie all the time.
Penny: I call everyone sweetie.
Sheldon: You tramp.

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: I thought you didn't like Facebook any more.
Sheldon: Don't be silly, I'm a fan of anything that tries to replace actual human contact.

Bernadette: I'm too small for Twister. And roller coasters. And sitting with my feet on the floor. Hope you enjoyed the prenatal cigarettes, Mom.

(Sheldon knocks on Penny's door three times)
Penny: Who do we love?
Sheldon: Penny. (Knocks 3 times)
Penny: Who do we love?
Sheldon: Penny. (Knocks 3 times)
Penny: Who do we love?
Sheldon: Penny.