I've had this happen a handful of times.

The worst case I've ever had though, and recently, was I entered a dungeon (The Vault) with 2/4 players being new to the duty, the healer and the a DPS were 1st timers and unsure of how things worked.

The 2nd DPS (NIN) wanted to speed run, but we were all very clear that were were taking time, and I was trying to explain mechanics etc.

The jerkoff got PISSED at me for taking "too long" and not pulling every mob in sight, ran ahead 3 times, died 3 times, blamed the healer, blamed me, kept running ahead and dying (eventually I just LET it happen).

Then, actually had the NERVE to tell me off and said "STOP TRYING TO GET COMMENDS AND LETS GO."

Seriously, this community sometimes.