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: 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.

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.