I've mained healer since my Arcanist was level 30 and that has only happened to me about once in the entire 15 months I've played this game.

I've DPSed in order to make the dungeon go faster and been kicked (in Haukke's manor even though nobody died) only because the tank was scared he would die. I've been called the worst healer for trying to help tanks become more skilled.

I've also been giving commendations though too for the exact same thing. I strongly believe in DPSing as a healer as much as humanly possible. If things are still going slowly, I look at the DPS' gear. Even one undergeared person due to them leveling or being a fresh 60/50 will make a huge DPS difference.

I do not cuss them out for that though. I think the key to understanding is communication. I always say hello and I always ask the tank if what he is comfortable doing what he is doing. Until a while ago, I would do Big pulls and sometimes die but at the start of the match I would always tell them I'm newer to tanking since I don't main tank class.