Sheldon: Worst Renaissance Fair ever!
Leonard: Please let it go, Sheldon.
Sheldon: It was rife with historical inaccuracies, for example, the tavern girl, serving flagons of mead, now her costume was obviously Germanic, but in 1487, the Bavarian purity laws, or Reinheitgebot, severely limited the availability of mead. At best, they would've had some spiced wine.
Leonard: You're nitpicking!
Sheldon: Oh, really? Well, here's another nit for you, the flagons would not have been made of polypropylene.

Leonard: Penny thinks I'm too smart for her. That's ridiculous!
Sheldon: I know! Most of your work is extremely derivative. And don't worry, that's not a secret.

Raj: I hate trains.
Sheldon: Oh, don't be silly. You love trains.

Penny: Look, just forget I told you about me not graduating from community college, okay?
Sheldon: Forget? You want me to forget? This mind does not forget. I haven't forgotten a thing since the day my mother stopped breast-feeding me. It was a drizzly Tuesday.

Penny: I meant has he ever been involved with someone who wasn't a brainiac?
Sheldon: Oh! Well, a few years ago, he did go out with a woman who had a Ph.D in French Literature.
Penny: How is that not a brainiac?
Sheldon: Well, for one thing she was French.

Sheldon: Waitresses don't yell at you at Big Boy.

Sheldon: A cuba libre traditionally comes in a tall glass with a lime wedge in it.
Penny: Then swim to cuba.
Sheldon: Bartenders are supposed to have people skills.

Sheldon: If it's good enough for Kirk, Crunch, and Kangaroo it's good enough for me.

Sheldon: If I could I would, but I can't so I shan't.

Sheldon: (Practising speaking Mandarin) Show me your citrus peels.
Penny: Sheldon?
*Sheldon freaks out in Chinese.*
Penny: I'm sorry. Look, do you have a second?
Sheldon: A second what? Pair of underwear?

Amy: Kiss me where I've never been kissed before?
Sheldon: You mean like Salt Lake City?

Sheldon: Geology isn't a real science!

Sheldon: Mmm. (In Mandarin) Your monkey sleeps inside me.

Sheldon: (Mandarin) Long live concrete? Thank you.

Penny: What I'm saying is, Leonard might be different in a good way. And obviously, my usual choices have not worked out so well.
Sheldon: Your last choice worked out for Koothrappali. He got a free iPod.