Sheldon: Leonard, you can't train my girlfriend like a lab rat
Leonard: Actually, it turns out I can
Sheldon: Well you shouldn't

Penny: I give up, he's impossible
Sheldon: I can't be impossible, I exist. I believe what you meant to say is, "I give up, he's improbable."

Penny: I'll tell you what, next french toast day, I'll make you oatmeal
Sheldon: Good lord, are you still gonna be here next french toast day?

Raj: I don't like bugs, okay? They freak me out.
Sheldon: Interesting. You're afraid of insects and women. Ladybugs must render you catatonic.

Raj: What happened?
Sheldon: Obviously another carnal fiasco with the 'Shiksee' goddess.
Howard: Shiksa. Shik-Sa.
Sheldon: Forgive me. Yiddish was not spoken in East Texas. And if it was, it wasn't spoken for long.

Howard, you know me to be a very smart man. Don't you think that if I were wrong, I'd know it?

Penny: You know, I do understand what you're going through.
Sheldon: Really? Did you just have the Nobel Prize in Waitressing stolen from you?

Hello, Penny. I realize that you're currently at the mercy of your primitive biological urges, but as you have an entire lifetime of poor decisions ahead of you, may I interrupt this one

Sheldon: It must be an emergency; everyone at the university knows that I eat my breakfast at 8 and move my bowels at 8:20
Leonard: Yes, how did we live before Twitter?

Sheldon: Why does Leonard get to go?
Wolowitz: Because he's upset over his situation with Penny, and if I have to hear about it again, I'm gonna kick him in his ovaries

I have to say I thought the toilet humor would get less funny with repetition. Apparently there is no law of diminished comedic returns when it comes to space poop

Sheldon: You have to check your messages, Leonard! Leaving a message is one-half of a social contract, which is completed by the checking of the message. If that contract breaks down, then all social contracts break down and we descend into anarchy.
Leonard: It must be hell inside your head.
Sheldon: At times.

TBBT Quotes

Oh, Bernadette, please play my clarinet.

Raj's poem

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?