What does Dwight mean by "vamping"?

I believe this was the weight loss episode. What does Dwight mean by the word vamping?

Michael: No, no, no, NO, no! You know what? Fat people are not monsters! Why don't you guys have a little more sensitivity to the subject. Bang! Boom! Case in point! Look at the outside of this building. It is ugly. But you come inside... and it is beautiful. Just like this unappealing fat suit. Inside is a rather handsome, sexy, man.

Dwight: Vamping.

Michael: Hey! Why don't you just sit down, please?

Dwight: Eh, I've been sitting all day.