Someone who turns a normally civil conversation or situation into something unpleasant or troublesome.
Disgruntled guy: Well I just got off work and I'm about to head home, so...
Homeless guy: Hey man could you give me a dollar
Disgruntled guy: Fuck off ya fag
Tim: John go get me a root beer
John: You can probably get up and get it yourself
Tim: Dude... don't be a fag
John: Don't call me a fag you ass master