same here. I just ignore them so that I never have to group with them again. I know I should say something, but more often than not, dps like that means i have no time to say anything without contributing to a wipe. and sometimes they have gotten me too annoyed to say anything.
This is the danger, yeah. It's usually not worth my time as Tank / Heals to argue with people who annoy me, especially since the type of player that gets flippant about group "etiquette" also tends to be belligerent and impatient if you try to discuss it with them. So, I just finish the run compensating for them, then put them on Ignore.
Then they start a thread on the forums asking why their DPS queue takes forever.