1) Too many of them (even one is too many for me) Leeroy their way through more enemies than they, healers, and DPS can handle at once.

2) Lately there have been bandwagon tanks trying to be DPS and neglecting the prime reason for being a tank, not to mention being an MP drain on healers.

3) For reasons I can't explain (Psych was not my major in college), tank jobs just attract idiots.