Mary Cooper: Sweetheart, your little friend is concerned about you.

Leslie: Listen Leonard, neither of us are neuro-scientists, but we both understand the bio-chemistry of sex, ... I mean: Dopamine in our brain is released across synapses causing pleasure. You stick electrodes in a rat's brain, give him an orgasm button and he'll push that thing 'till he starves to death.
Leonard: Who wouldn't?

Sheldon: (Knocking on Penny's door early in the morning). Penny, Penny, Penny!
(Penny opens the door).
Sheldon: Good morning.
Penny: Do you have any idea what time it is?
Sheldon: Of course I do. My watch is linked to the atomic clock in Boulder, Colorado. It's accurate to one-tenth of a second, but as I'm saying this it occurs to me once again your question may have been rhetorical.

Leonard: New neighbor?
Sheldon: Evidently.
Leonard: Significant improvement over the old neighbor.
Sheldon: A 200 pound transvestite with a skin condition, yes, she is.

Leonard: Sheldon, why is this letter in the trash?
Sheldon: Well, there's always the possibility that a trash can spontaneously formed around the letter, but Occam's Razor would suggest that someone threw it out.

Sheldon: I don't care if anybody gets it. I'm going as the Doppler Effect.

Sheldon: I'll watch the last 24 minutes of Doctor Who, although at this point it's more like Doctor Why Bother.

Kurt: You are lucky little dwarf.
Sheldon: He is a hobbit! Don't worry, I've got your back!

Leonard: Come on, guys, push!
Howard: If I push any harder I'm gonna give birth to my colon.

Sheldon: I couldn't sleep knowing that just outside my bedroom is our living room and just outside our living room is that hallway and immediately adjacent to that hallway is [Penny's messed up apartment]!
Leonard: Do you realize if Penny wakes up there's no reasonable explanation to why we are here?
Sheldon: I just gave you a reasonable explanation.
Leonard: No, no. You gave me an explanation. Its reasonableness will be determined by a jury of your peers.

Penny: Cool! Whose head did I just blow off?
Sheldon: Mine!

Sheldon: Mmm. [in Mandarin] Your monkey sleeps inside me.

Janitor: The answer is minus eight pi alpha.
Sheldon: Hang on a second, that's not our answer. What are you doing?
Janitor: Answering question, winning Physics Bowl.
Sheldon: How do you know anything about physics?
Janitor: Here, I am janitor. In former Soviet Union, I am physicist. Leningrad Politechnika. Go Polar Bears!

Sheldon: Damn you, walletnook.com!
Leonard: Problem?
Sheldon: The online description was completely misleading. They said 8 slots plus removable ID. To any rational person, that would mean room for nine cards. But they don't tell you the removable ID takes up one slot. It's a nightmare!

Sheldon: I'm taking a sabbatical because I won't kowtow to mediocre minds.
Penny: So you got canned, huh?
Sheldon: Theoretical physicists do not get 'canned'. But yeah.