Penny: I need some guinea pigs.
Sheldon: Okay, there's a lab animal supply company in Reseda you can try. But if your research is going to have human applications, may I suggest white mice? Their brain chemistry is far closer to ours.
Penny: I swear to God, Sheldon, one day I'm going to get the hang of talking to you.
Leonard: His mom's been saying that for years.

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: I don't believe it. What's gotten into him?
Penny: Oh, maybe a couple of virgin Cuba Libres that turned out to be kinda slutty.
Leonard: You didn't.
Penny: Hey, you do your experiments, I do mine.

Raj: How can I be a gynaecologist? I can barely look a woman in the eye!

Sheldon: How often does one see a beloved fictional character come to life?
Wolowitz: Every year at ComiCon. Every day at Disneyland. You can hire Snow White to come to your house. Of course they prefer if you have a kid.