I used to play in a metal band too!

I used to have buddies like this too. They'd go from being the coolest people in the world, to putting you down so they are the "star" of the show. They feel a sense of power poking fun at others. They also get a big laugh from their audience, so that incourages them more.

Been around them a lot, and yes, they suck. Tell him to bugger off next time. Be serious about it but don't be a prick either. Some people get quite surprised when some people are blunt with them.