Leonard:What am I supposed to say? Sure, Penny, I'm cool with having your old boyfriend sleep in your apartment.
Leonard imitating Penny: Well, Leonard, it doesn't matter if you're cool or not, 'cause I'm penny and I'm pretty and I can do whatever the hell I want.

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.

Sheldon: This song is never going to stop. Have you ever dealt with something so relentlessly irritating?
Leonard: That's a trick question, right?

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.

Sheldon: Stop it both of you! All this fighting, I might as well be back with my parents!
*Imitating his Mom* Dammit, George! I told you if you didn't quit drinking I would leave you!
*Imitating his Dad* Well, I guess that makes you a liar, because I'm drunk as hell and you are still here!
*Imitating his Mom* Stop yelling, you're making Sheldon cry!
*Imitating his Dad* I'll tell you what is making Sheldon cry, that I let you name him SHELDON!

Sheldon: You can't make a half sandwich. If it's not half of a whole sandwich, it's just a small sandwich.

Sheldon: Leonard, when that woman moved in three years ago I told you not to talk to her, and now look. We're going to be late for the movies.