I could get half of my program to back me up about this guys' behavior.

But you're right, his behavior is definitely affecting us on an academic level; we spent an hour trying to agree on the phrasing of a single hypothesis. We would have been done in 10 minutes if he hadn't been there.

I'll definitely approach my group about talking to the prof. Last semester, this guy worked alone from my group, because he also couldn't agree on our research focus. If it wasn't his way, then it was totally incorrect, and he wouldn't (and isn't) amenable to compromises.

And he outright tells people that their desire to study something is worthless or stupid.