Penny [about his mom]: You can't let her get into your head
Leonard: It's too late for me, my head is her summer house

Mrs. Hofstadter [about Penny]: If you want to have sex with that woman, find out what kind of cologne her father wore
Leonard: Hello mother

Leonard: Okay, is everyone clear on the plan?
Wolowitz: Yes. Koothrappali is going to wet himself, I'm going to throw up, Sheldon is going to run away, and you're going to die. Shall we synchronize our watches?

Leonard: What was the plan?
Penny: Um, waitress for six months and then become a movie star.
Leonard: Was there a Plan B?
Penny: TV star.

Penny: Dave is not smarter than you, he's an idiot.
Leonard: Really? Why would you say that?
Penny: Because a smart guy takes the nude photos of his wife off his cell phone before he tries to take nude photos of his girlfriend.
Leonard: He tried to take nude photos of you?
Penny: That's what you took from that?

Leonard: Every time I try to talk to her about moving out she cries, and we have sex.
Raj: You're lucky. With me it's usually the other way around

Penny: You don't always have to go along with what the woman wants.
Leonard: Huh.
Penny: What?
Leonard: Nothing... just re-thinking my whole life

Penny: I am going to introduce your friend to a world of hurt.
Leonard: You don't want to get into it with Sheldon. The guy is one lab accident away from being a super villain

Raj: We now have the address of the Top Model house.
Howard: God bless you, Google Street View—registered trademark.
Leonard: Okay, for the record, what you guys are doing is really creepy.
Wolowitz: You know what? If it's creepy to use the Internet, military satellites, and robot aircraft to find a house full of gorgeous young models so that I can drop in on them unexpectedly, then fine, I'm creepy.

Leonard: Put it on the agenda.
Sheldon: You have to make a motion to put it on the agenda.
Leonard: Oh, I'll make a motion, but you're not going to like it

Leonard: Just apologize to him, okay?
Penny: What? I'm not going to apologize to that nut-case.
Leonard: Come on, it's easy. He'll even tell you what to say

Wolowitz: Over the years, we've formulated a number of theories about how he might reproduce. I'm an advocate of mitosis.
Penny: I'm sorry?
Wolowitz: I believe one day Sheldon will eat an enormous amount of Thai food and split into two Sheldons.
Leonard: On the other hand, I think Sheldon might be the larval form of his species and someday he'll spin a cocoon and emerge two months later with moth wings and an exoskeleton

TBBT Quotes

Penny, there's only one cookie with something in the middle that solves life's problems, and that's an Oreo. Or a Nutter Butter, if you're in a pinch.

Sheldon

Penny: Here's a question-- as an alien pretending to be human, are you planning to engage in any post-prom mating rituals with Amy?
Sheldon: There are post-prom mating rituals?
Penny: Not always. Unless your date drives a van with an air mattress, then always.
Sheldon: Well, if it's part of the prom experience, then I'm open to it.
Penny: You're kidding.
Sheldon: I may be an alien, but I have urges.If Amy wants to copulate by firing her eggs into space, well, then, I will happily catch them with the reproductive sac on my upper flermin. I'm not the best at reading facial cues, but I can see that you're a little turned on.