Penny: Wait a minute. You mention his birthday and he vanishes?
Leonard: Well, where's that information been this whole time?

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.

Penny: So what's going on?
Sheldon: I don't know. I looked around the room, and I saw all the faces and the presents, and it it was just too much.
Penny: I get that. Hey, you want to just bring a few people in here? You know, Wil Wheaton in the bathtub, Batman on the toilet. It'll be like the weirdest Comic-Con ever.

Leslie Winkle: Uh, in the past, I would've said something obnoxious, like, "Happy birthday, dumbass". But I'm not gonna do it. You and I have both grown a lot, and it's just so nice to see you all again. So happy birthday, Sheldon.
Sheldon: Oh. Oh, now, you know I hate change. Say it.
Leslie Winkle: Happy birthday, dumbass!

Sheldon: I don't think I can go back out there.
Penny: That's fine. You know, I hate that your sister and her friends used to torture you. But what I hate even more is, if I was there, I would have tortured you, too.
Sheldon: Based on this pep talk, I'd say you're still doing it.
Penny: My point is, there was a time I never would've been friends with someone like you, and now you are one of my favorite people. So, if what you need is to spend your birthday in a bathroom, I'm happy to do it with you.
Sheldon: Well, everyone will think I'm weird.
Penny: Sweetie, you are weird. Everyone knows you're weird, but they're all still here because they care about you so much.