The only word in the English language that can be used under ANY circumstance. Its a dismissive response to a question that cannot be answered, a furious response to a statement you do not believe, a way of pretending you understood something you didn't, a way of shrugging off an insult, and anything/everything else.
Conor Courtney: Bro dude that dude girlfriend bro of GOD DAMN I WOULD RAPE THAT!
Mr. Kravitz: Macken whats the answer to this question?
Mr. Kravitz: Macken this is serious your failing this class
Macken: Hey uhm hi uhm do you want to uhm err go out with me?
Girl: Well I would and all but I don't think your my type, I'm going through a bad patch, I'm trying to say single, I just went through a bad break up, I was born a man-
Robber: Give me all your money right f***ing now
Macken: Pshaw pshaw pshaw pshaw PSH-AWWWW!!!!