Sheldon: Biologically speaking, Howard is perfectly justified in seeking out the optimum mate for the propagation of his genetic line. Howard: Thank you, Sheldon. Sheldon: And whether that propagation is in the interest of humanity is, of course, an entirely different question.

Sheldon: Cause of Injury: Lack of Adhesive Ducks.

Sheldon: You keep in mind that my sharply-worded comments on Yelp.com recently took down a muffin store.

Sheldon: Why do you have the Chinese character for 'soup' tattooed on your right buttock?
Penny: It's not 'soup'; it's 'courage'.
Sheldon: No it isn't. But I suppose it does take courage to demonstrate that kind of commitment to soup.
Penny: How'd you see it? You said you wouldn't look.
Sheldon: Sorry. As I told you, the hero always peeks.

Sheldon: Stop it both of you! All this fighting, I might as well be back with my parents!
*Imitating his Mom* Dammit, George! I told you if you didn't quit drinking I would leave you!
*Imitating his Dad* Well, I guess that makes you a liar, because I'm drunk as hell and you are still here!
*Imitating his Mom* Stop yelling, you're making Sheldon cry!
*Imitating his Dad* I'll tell you what is making Sheldon cry, that I let you name him SHELDON!

Sheldon: Leonard, when that woman moved in three years ago I told you not to talk to her, and now look. We're going to be late for the movies.

Sheldon: I should have asked for much more than a comic book and a robot.

Sheldon: You can't make a half sandwich. If it's not half of a whole sandwich, it's just a small sandwich.

Sheldon: There once was a brave lad named Leonard.
With a fi fi fiddle dee dee.
He faced a fearsome giant.
While Raj just wanted to pee.

Sheldon: Excuse me. You're misusing the word 'ho'. It's an interjection used to call attention to a destination, not an object, as in 'land ho' or 'westward ho'.

Howard: Are you familiar with the Drake Equation?
Sheldon: The one that estimates the odds of making contact with extraterrestrials by calculating the product of an increasingly restrictive series of fractional values such as those stars with planets, and those planets likely to develop life? N equals R times FP times NE times FL times FI times FC times L?
[pause]
Howard: Yeah, that one.

Sheldon: There was a tall man from Cornwall
Whose length exceeded his bed.
"My body fits on it.
But barely upon it.
There's no room for my big Cornish head!"

Sheldon: I am uncomfortable having been included in your lie to Penny.
Leonard: What was I supposed to say?
Sheldon: You could have told her the truth.
Leonard: I could not have said that, it would have hurt her feelings.
Sheldon: Is that a relevant factor?
Leonard: Yes.
Sheldon: Then I suppose you could have agreed to go.
Leonard: What would I have said afterwards?
Sheldon: I would suggest something along the lines of "singing is neither an appropriate vocation nor avocation for you and if you disagree, I recommend you do a CAT scan to locate the tumor which is pressing on the cognitive processing center of your brain".

Sheldon: There's a fine line between wrong and visionary. Unfortunately, you have to be a visionary to see it.

Sheldon: Like the subordinate male protagonist in countless action movies who disappears halfway through the second reel, I have returned to save the day. [pause]. Odd, he's usually met by cheers.