I primarily tank DF groups. The thing that annoys me about people more than anything are those who don't admit to not having done a dungeon before (especially at level 50). I'm more than happy to explain fights to people but I assume you know the place unless you tell me otherwise.

I usually don't rage at groups but I'm mentally evaluating things. For example, when I enter a dungeon and see DPS and/or the healer with less than 3K HP, I know it's likely we're in trouble. Even if the person is skilled and knows the instance, a certain gear threshold is needed to bypass certain checks (particularly things like the Demon Wall).

Personally though, if I can give advice to fix the problem, I do so. If I see that there is an underlying problem (like lack of gear that won't allow us to progress and we do, in fact, wipe on something like Demon Wall), I just drop the group. 15 minutes isn't that long.