There was also a bit about tanks not biting off more than they can chew.

But yes, DPS needs to understand how threat works, how the mechanics of tanking work with their abilities, and how the mob's damage gets delivered.

When I'm healing instances on the way to 85 (resto druid levl 71 now and coming from a rogue main) I'm always having to "advise" the melee classes who want to stand next to their tank and fight the good fright from the front. I have to explain how parry works and that most melee mobs are also able to cleave. Then I have to explain that because of all of this he's compounding damage on himself and on the tank which burns through my mana.

Most of this conversation happens during the silence of the wipe that I couldn't heal through and after I'm accused of being a shitty healer. If I stick around after the wipe I either see them take my advice and learn why rogues do it from behind OR we rinse, repeat, and wipe again and I do a /rude, apologize to the rest and drop group.

(Of course, after cataclysm nobody is playing their early 70s so my queue times aren't insta-cast anymore and I sometimes just vote to kick.)