Sheldon: Who's ready to laugh? [Leonard groans] Okay. So Feynman, Einstein and Schrodinger walk into a bar. Feynman says, "It appears we're inside a joke." Einstein replies, "But only to an observer who saw us walk in simultaneously." To which Schrodinger says, "If someone's looking in the window, I'm leaving."
Leonard: [chuckles] That's actually funny.
Raj: You should send that to Jimmy Fallon.

Sheldon: Can I respond now?
Leonard: Do it.
Sheldon: You mess with the bull, you get the horns. I'm about to show this guy just how horny I can be.
Leonard: Somebody else do it.

Penny: Oh, big deal. Not knowing is part of the fun.
Sheldon: "Not knowing is part of the fun." Was that the motto of your community college?

Penny: The Flash shirt is what? Because you're gonna run really fast?
Sheldon: No, the Flash shirt is because it's Friday. But it's nice when things work out.

Sheldon: I'm exceedingly smart. I graduated college at fourteen. While my brother was getting an STD, I was getting a Ph.D. Penicillin can't take this away.

Sheldon: They're very different. Physics answers the question: what is the nature of the universe? Geology answers the question: you know, what'd I just trip over?

Zack: You know, I saw this great thing on the Discovery Channel. Turns out if you kill a starfish it'll just come back to life.
Sheldon: Was the starfish wearing boxer shorts? Because you might have been watching Nickelodeon.

Sheldon: I'd like to go over some proposed changes to the roommate agreement, specifically to address Penny's annoying personal habits.
Penny: Oh my God! What personal habits?
Sheldon: I have a list. FYI overuse of the phrase "Oh my God" is number 12.

Penny: So what do you say Sheldon, are we your X-men?
Sheldon: No, the X-men were named for the X in Charles Xavier. Since I am Sheldon Cooper, you will be my C-men.

Sheldon: I wouldn't tell you the secret. Sssh!
Leonard: What secret? Tell me the secret.
Sheldon: Mom smokes in the car. Jesus is okay with it, but we can't tell dad.
Leonard: Not that secret, the other secret.
Sheldon: I'm Batman! Ssssh!

Howard: Are you listening to yourself?
Sheldon: I always listen to myself. It's one of the great joys of my life.

Sheldon: *singing in the tune of "Eye of the Tiger"* It's the eye of the tiger, it's the ear of the bat. It's the whiskers of a catfish and the walrus--
Howard: Hang on. Not that your song isn't terrible-- it is... but how do you mention bats and leave out sonar?
Sheldon: You didn't let me finish. *singing* And also regarding the bat. It has sonar.

Sheldon: Oh gravity, thou art a heartless bitch.

Sheldon: Checkmate.
Leonard: Oh, again?
Sheldon: Obviously, you're not suited for three dimensional chess. Perhaps three dimensional Candy Land would be more your speed.
Leonard: Just reset the board!
Sheldon: It must be humbling to suck on so many levels.

Penny: You guys just got back together. You might not want to ditch her on her birthday.
Leonard: I think Penny has a point. You can see it another day.
Sheldon: But someone might spoil the movie. No one can spoil Amy's birthday for me. Surprise, she's even older. Who saw that coming?
Penny: Aww, that's nice. Put that on her cake.