I got kicked recently for tanking with str accesories and dropping tank stance on bosses with a heal onry healer. He said wannabe dps tanks trigger him. I told him healers that don't dps trigger me. Shortly after that I was removed from duty.
Atleast I could laugh about it.

Another time I was healing as a scholar and dpsing during mass pulls, tank would often dip below 3k hp before I healed him. I made sure he never died while still contributing to dps, yet he took offense to being below half health allot and starting raging at me. He told me I suck because I can't keep his hp up. I tried to explain what I was doing, but got kicked before I could finish.

Tldr;
Some terrible players can't handle good play and kick the good player.