Snap

A slang expression, used in response to someone being insulted or giving a particularly good comeback.

Leonard: (about Kurt) If he were any bigger, he'd have moons orbiting him.

Sheldon: Oh, snap.

This exchange is interesting because in later episodes Sheldon demonstrates extreme awkwardness with modern slang expressions (0209), and even shows that he doesn't understand what "snap" means in this context (0208):

Sheldon: (in reference to calling AAA to service the malfuntioning Mars lander) You have to be standing next to your vehicle with your card when they arrive.

Raj: Oh, snap.

Sheldon: (checking his clothing for something loose) Snap what?

Sheldon has become more comfortable with the term, however. Raj whispers it to him after he compares Leonard's work to third graders growing lima beans in wet paper towels. Sheldon responds:

"While I appreciates the 'Oh snap', I'm uncomfortable having your moist breath in my ear" (0310).