Actually I'm just being silly, but I noticed this morning that Tybalt's first two lines, literally, are "What?"
What, are thou drawn among these heartless hinds?
Turn thee, Benvolio, look upon they death.
I do but keep the peace: put up they sword,
Or manage it to part these men with me.
What, drawn, and talk of peace! I hate the word,
As I hate hell, all Montagues, and thee:
Have at thee, coward!
Reminds me of a neighborhood bully when we were growing up. Whenever you said something that he felt like taking as insulting he'd always start with a "What?" Far from being intimidating, it only made him seem stupid, like he was never fully able to process that he'd been insulted. There used to be a pro-wrestler who did a whole big gimmick out of punctuating his interviews with "What?" whenever somebody else was talking.
I realize of course that it is not being used in that context. It's actually a pretty common interjection in Shakespeare's dialogue, I count 14 times in R&J alone. Taming of the Shrew has 22!