Well XP awards for RP are a touchy subject.
Some people play the game for role playing and some play it to blow off some steam by smacking some baddies (roll playing) because of this in a mixed group the people who are not into the role playing aspect of the game feel cheated when the role players get extra XP and they don't, in theory this should encourage role playing but some people don't take it well.
I have a mixed group like that and what I do which seems to work out well is that at the end of the module I give out extra XP not only for role playing your character well but also for combat related achievements; things like doing the most damage in one hit, killing the most baddies, making the most incredible shot, taking the most damage and even dying.
This way the folks who RP get rewarded for their RP skills and the folks who just want to apply the smack down get rewarded for doing exceptionally well in that department.
Everyone wins and no whining.
As for the DM you mentioned he sounds like a jerk. Not being prepared for the session is not cool, it wastes peoples time and kills the fun of the session.