Probably "twat" in "All Alone" from Spamalot... Perfectly vulgar, and unexpected.
This is a little off topic, but a word I've always wanted to put in a mock-shakespearian script (as a name) is Fellatio. Does that not ever strike some people as amusing? Perhaps it's my vulgar sense of humor... But you must admit, there are quite a few good jokes that could come of it!
I hold a degree in Musical Theatre from Montclair State University. It is useless. Now I'm funny for money. Oh, and I sing.