Sheldon: Come on out, merry pranksters. Take a bow!

Sheldon: "See you in hell Sheldon"? The most frightening thing about that is the missing comma.

Mary: Just because a cat's got kittens in the oven doesn't make 'em biscuits.

Sheldon: You know, the German philosopher Friedrich Nietzsche believed that morality is just a fiction used by the herd of inferior human beings to hold back the few superior men.
Leonard: Thanks, that actually does help.
Sheldon: It's worth noting that he died of syphilis.

Sheldon: I am also a son of the Lone Star state. I'm Texas through and through. And we know how to settle scores down there. If you doubt me, just ask Mexico.

Wolowitz: (To Leonard) Did I just see you pick up a girl in a comic book store?
Stuart: Because if you did, you get your picture up there, on the Wall of Heroes.

Sheldon: [jumps out of the sofa] Bazinga, punk. Now we're even!

Leonard: More Halloween candy. Didn't you just buy a bunch of it yesterday?
Penny: Oh, yeah. That's gone. It's a rough month when Halloween and PMS hit at the same time.

Sheldon: It's me, Mrs. Wolowitz.
Howard: That's not my mom, it's Bernadette.
Sheldon: Really? That's very unsettling.

Sheldon: All right, so the topic at hand is sexual fidelity. Probably won't be relying on Suess here. Although One Fish Two Fish, Red Fish Blue Fish might be surprisingly applicable here.

Raj: (Talking to the snake) Let's go to the biology lab and find you some nice yummy mice.
Sheldon: I tried to scare an Indian with a snake. Come on, Cooper. You're better than this.

Amy: You are aware that your ritualistic knocking behavior is symptomatic of obsessive-compulsive disorder?
Sheldon: Is not. Is not. Is not.
Amy: Denial. Denial. Denial.

Sheldon: Frankly, Mom, I'm encouraged to see how advanced your group has become -- willing to sail into the ocean without fear of falling off the edge.

(Howard has just told Mary about his upcoming trip to the International Space Station.)
Mary Cooper: I bet your mom is really proud of you.
Howard: Nope. She says if I don't back out, she's gonna go on a hunger strike. It'd take years before she'd be in any kind of danger, but still.

Mary: Oh, it is a hoot and a half. You write your sins on a clay pigeon, they fire 'em up in the air and you pulverize 'em with a twelve gage shotgun full of our Lord's forgiveness.