Penny: I'm a Sagittarius, which probably tells you way more than you need to know.
Sheldon: Yes, it tells us that you participate in the mass cultural delusion that the sun's apparent position relative to arbitrarily defined constellations at the time of your birth somehow affects your personality.
Penny: Participate in the what?

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.

Leonard: Our babies will be smart and beautiful.
Sheldon: Not to mention imaginary.

Penny: So, what do you guys do for fun around here?
Sheldon: Well, today we tried masturbating for money.

Sheldon: Um, Penny, that's where I sit.
Penny: So, sit next to me.
Sheldon: No, I sit there.
Penny: What's the difference?
Sheldon: "What's the difference"?
Leonard: Here we go.
Sheldon: In the winter that seat is close enough to the radiator to remain warm, and yet not so close as to cause perspiration. In the summer it's directly in the path of a cross breeze created by open windows, there and there. It faces the television at an angle that is neither direct, thus discouraging conversation, nor so far wide to create a parallax distortion. I could go on, but I think I've made my point.