In the vast majority of cases when I see a tank having problems I give them some simple pointers and things usually work out.
There have been only a few cases where I simply couldn't take it anymore and dropped party:
- A Paladin in Dzemael that didn't use Shield Oath and never talked. Our Bard (from my FC) tanked the first boss and then we left. I really think that he hadn't even done the quest to unlock it.
- A Paladin in Garuda NM that wouldn't pull Garuda away from the stones. He talked, but in Italian, and I couldn't get him to understand me.
- A Monk in the level 40 guildhest where you have to kill the 5 demons at roughly the same time. Kept killing one of the demons even though we kept telling him to stop. Wouldn't talk.
There are limits to my patience, and if the other guy can't communicate with me, I just give up.