Sheldon: Leonard is upstairs right now with my archenemy.
Penny: Your archenemy?
Sheldon: Yes: the Dr. Doom to my Mr. Fantastic, the Dr. Octopus to my Spiderman, the Dr. Sivana to my Captain Marvel...
Penny: OK, I get it, I get it...
Sheldon: You know, it's amazing how many supervillains have advanced degrees. Graduate schools should do a better job of screening those people out.
The Codpiece Topology [2.02]
Howard: Not Sheldon. Over the years we've formulated a number of theories about how he might reproduce. I'm an advocate of mitosis.
Penny: I'm sorry?
Howard: I believe one day Sheldon will eat an enormous amount of Thai food and split into two Sheldons.
Leonard: On the other hand, I think Sheldon might be the larval form of his species and someday he'll spin a cocoon and emerge two months later with moth wings and an exoskeleton.
Penny: Okay, well, thanks for the nightmares.
The Cooper-Nowitzki Theorem [2.06]
Sheldon: Oh, look! Saturn III is on.
Raj: I don't want to watch Saturn III. Deep Space 9 is better.
Sheldon: How is Deep Space 9 better than Saturn III?
Raj: Simple subtraction will tell you it's six better.
Leonard: Compromise. Watch Babylon V.
Sheldon: In what sense is that a compromise?
Leonard: Well, 5 is partway between 3 and…never mind.
Raj: I'll tell you what. How about we go 'Rock-Paper-Scissors'?
Sheldon: Ooh, I don't think so. Anecdotal evidence suggests that in the game of 'Rock-Paper-Scissors', players familiar with each other will tie 75-80% of the time due to the limited number of outcomes. I suggest 'Rock-Paper-Scissors-Lizard-Spock'.
Sheldon: It's very simple. Look -- Scissors cuts Paper, Paper covers Rock. Rock crushes Lizard, Lizard poisons Spock. Spock smashes Scissors, Scissors decapitates Lizard. Lizard eats Paper, Paper disproves Spock, Spock vaporizes rock, and as it always has, Rock crushes Scissors.
Raj: …Okay. I think I got it.
Sheldon & Raj: Rock-Paper-Scissors-Lizard-Spock! [both play Spock and groan in frustration]
--The Lizard-Spock Expansion [2.08]