Howard: I did a stupid thing.
Leonard: Yeah, I guessed that.
Howard: It was the kind of thing that makes it kind of hard to face her now.
Leonard: That covers anything from farting in bed to killing a homeless guy. Oh my God, you ran over a hobo.

Leonard: Penny, as a scientist, my job is to figure out why things happen. But I don't think I'll ever understand how someone like me could get to be with someone like you. You know maybe I don't need to understand it, I just need to be grateful. I love you, Penny.

Leonard: What would you be if you were attached to another object by an inclined plane, wrapped helically around an axis?
Sheldon: Screwed?
Leonard: There you go.

Leonard: My point is, while you're spending all this time on your own, building computers or practicing your cello, what you're really doing is becoming interesting. When people finally do notice you, they're gonna find someone a lot cooler than they thought. And for those of you that were popular in high school, it's over, sorry. Thank you. Congratulations.

Leonard: Sometimes your movements are so lifelike I forget you are not a real boy.

Raj: Oh, you're so arrogant. If you were a super hero your name would be Captain Arrogant. And do you know what your super power would be? Arrogance.

Sheldon: Oh, Penny. Penny.
Penny: What's up?
Sheldon: Nothing. I just wanted to make Raj stop talking.