I have a relatively simple philosophy when it comes to mentoring.

-no need to say mechanics unless it's not blantantly obvious
-I only answer questions when asked
-don't comment on someone's gameplay unless it's really hindering the group.

I don't comment on healer/tank or even the dps' dps. As long as they're doing something and not sitting there I don't really care.

Does it frustrate me when the healer doesn't dps? Yes. Does it annoy me when the tank doesn't go out of tank stance to dps? Yes. Does it annoy me that the dps don't aoe? Yes. I always try to optimize myself in dps. I know what I'm doing is making the run go faster. If anyone asks, then yeah I'll tell them, because that most likely means that they do want to get better and won't get butthurt

I've just learned to not expect much from people.