Tanks get mad because we're blamed for EVERYTHING.

Healer D/Cs midfight? Tank's fault.
DPS can't count? Tank's fault.
DPS stood in fire? Tank's fault.
Healer stands in fire? Tank's fault.
DPS decides to go all leroy jenkins and gets eaten while everyone else is discussing strategy for the boss? Tank's ****ing fault.

Maybe take some responsibility for your own **** ups now and again and we won't be so damn angry all the time.