Leonard: Sheldon, are you worried about your safety?
Sheldon: No, I imagine if you were going to kill me, you'd have done it a long time ago.
Leonard: That's very true

Leonard: We're going to Long Beach?
Sheldon: No, of course not. There's no Cousin Leo; there's no intervention. Focus, Leonard.
Leonard: Oh, come on.
Sheldon: We just leave the house on Friday night, and we return in the wee hours, emotionally wrung out from the work of convincing Leo to go back into rehab.
Leonard: So, he goes back into rehab?
Sheldon: Yes, but he can relapse if Penny ever invites us to hear her sing again

Leonard: Alright, get some rest and drink plenty of fluids.
Sheldon: What else would I drink? Solids? Gases? Ionized plasma?
Leonard: Drink whatever you want

Sheldon: Checkmate.
Leonard: Argh, again?
Sheldon: Obviously you're not well-suited for three-dimensional chess. Perhaps three-dimensional Candyland would be your speed

Leonard: Sheldon, don't you think you're overreacting?
Sheldon: When I'm lying comatose in a hospital, relying on inferior minds to cure me, these Jell-O cultures and my accompanying notes will give them a fighting chance

Leonard: You speak English really well.
Dennis: So do you... except for your tendency to end sentences with prepositions.
Leonard: What are you talking about?
Dennis: That.
Sheldon: He's not wrong

Wolowitz: We need a hot 15-year-old Asian girl with a thing for smart guys.
Penny: What?
Leonard: Howard, that's racist. Any fifteen year old girl will do the trick

Leonard: Come on, Dennis, I'll show you the rec center. They've got Nautilus equipment.
Dennis: Do I look like I lift weights?
Leonard: Not heavy ones

Sheldon: Here's the problem with teleportation.
Leonard: Lay it on me.
Sheldon: Assuming a device could be invented, which would identify the quantum state of matter of an individual in one location and transmit that pattern to a distant location for reassembly. You would not have actually transported the individual, you would have destroyed him in one location and recreated him in another.
Leonard: How about that.
Sheldon: Personally, I would never use a transporter because the original Sheldon would have to be dissintegrated in order to create a new Sheldon.
Leonard: Would the new Sheldon be in any way an improvement on the old Sheldon?
Sheldon: No, he would be exactly the same.
Leonard: That is a problem

Raj: We need a social catalyst.
Leonard: Like what? We can't get 15-year-old girls drunk.
Wolowitz: Or can we...!?

Sheldon: What happens if you use argon lasers instead of helium-neon?
Leonard: It would blow up!
Sheldon: Are you sure?
Leonard: Pretty sure...
Sheldon: Pretty sure? It's not very scientific. Is this how you normally work? Just hunches and guesses and stuff?

Leonard: At least I didn't have to invent 26 dimensions just to make the math come out.
Sheldon: I didn't invent them, they are there!
Leonard: In what universe?
Sheldon: In all of them, that's the point

TBBT Quotes

Sheldon [to Kripke]: Also, I am given to understand that your mother is overweight.
Raj: Oh, snap.
Sheldon: Now of course, if that is the result of a glandular condition and not sloth and gluttony then I withdraw that comment.

How is "doable" anything but a compliment?

Wolowitz