Leonard: I'm sorry.
Raj's sister: Why do you say that?
Leonard: When I'm in bed with a girl, that's just my natural response.

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: Hands off my sister.
Sheldon: Why would I touch your sister? She's all covered in airplane germs.

Sheldon: And to think, I was about to waste the last of my good haemorrhoid cream on you.

Raj: I can't believe you kissed my sister with moth mouth.
Leonard: Well, I can't believe you'd use Sheldon's toothbrush.
Sheldon: You used my toothbrush?
Raj: Not the brush part. Just the little rubber thing to pick food from my teeth and massage my gums.