Leonard: I'm sorry, but facts are facts.
Penny: Right, and if you can't understand it, it's not a fact.
Leonard: No, if it's not a fact, it's not a fact.

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

Raj: You can't wear the hands on the date.
Sheldon: Hulk sad!

Penny: You know, I believe in ghosts, too.
Leonard: Great.
Penny: And astrology.
Leonard: I know, and pyramid power and healing crystals.
Penny: Oh, no, no, no, crystals don’t work.
Leonard: Really, that’s the line? Psychics are real, but crystals are voodoo?
Penny: Oh, Voodoo is real. You don't want to mess with Voodoo.

Leonard: How can I go out with a woman who believes in psychics?
Howard: Hey, I once dated a girl who believed she was abducted by aliens.
Leonard: And that didn't bother you?
Howard: Au contraire. It meant that she was gullible and open to a little probing.