Amy: Goodnight, Stuart.
Stuart: Goodnight.
*Stuart and Amy hug*
Sheldon: (From inside Amy's apartment) Take the hint, Stuart, the lady said goodnight!

Sheldon: I'll have a diet Coke.
Penny: Can you please order a cocktail? I need to practice mixing drinks.
Sheldon: Fine. I'll have a virgin Cuba Libre.
Penny: That's rum and Coke, without the rum?
Sheldon: Yes, and would you make it diet?

Sheldon: Amy Farrah Fowler has asked me to meet her mother.
Leonard: Yeah, so?
Sheldon: What does that mean?
Leonard: Well, you know how you're always saying Amy is a girl who is your friend but not your girlfriend?
Sheldon: Uh huh.
Leonard: Well, you can't say that any more.

Sheldon: Would you like some aloe vera? 'cause you just got burned.

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

Sheldon: You know, I do recall seeing some female undergarments. Where was that? Oh, yes. Earlier this evening, I happened to gaze out the window and a brassiere caught my eye. Do those look familiar?

Leonard: It's 3 in the morning!
Sheldon: 3 in the morning is a good time for bongos.
Leonard: I was sleeping!
Sheldon: Leonard sleep while I play bongos.
Leonard: No, I don't.
Sheldon: Leonard no sleep while I play bongos.

Sheldon: Einstein defined insanity as doing the same thing over and over again and expecting different results. By that definition, Penny is cuckoo for Cocoa Puffs.

Sheldon: As a native Texan, I must say I've never heard the phrase "yeeehaw" used in quite that context.

Howard: You gotta like this: the girlfriend, the ex-girlfriend, bonding over your rooty-tooty stinky booty? (All but Leonard laugh)
Leonard: Kill me.
Sheldon: It wouldn't help. The human body is capable of being flatulent for hours after death.

Sheldon: Sorry, I'm late.
Leonard: What happened?
Sheldon: Nothing. I just didn't want to come.

Penny: This has gotten way out of hand, okay. I've done some stupid things, you've done some stupid things. How about we just call it even, and move on with our lives?
Sheldon: I've done no stupid things.
Penny: Look, you've gotta meet me halfway here.
Sheldon: I am meeting you halfway. I'm willing to concede that you've done some stupid things.

Sheldon: There's no need to interact with me. I'm just here to observe.

Penny: Hey. Nice knees.
Sheldon: Thank you! They're my mother's.

Penny: Hey Sheldon, whattcha got there a new comic book?
Sheldon: Old comic book. I just got it from the safe deposit box.
Penny: What do you have a safe deposit box for?
Sheldon: Old comic books.