Tactful ways to inform people that they're playing badly?

[Granyala]

An LB 1 used by a dps is useful because it actually does something. A small something, perhaps, but still something.

Sure, but honestly: in a dungeon is't not worth getting worked up about it.
Advise the player (though most will start to intentionally work against you after that just because they can do it to spite you) and then move on.

Imho they could patch out the LB 1 and 2 altogether, usually I tease our DPS in TS with "Did you miss again? I didn't see the HP bar move" because the damage of these 2 is so ... well.. lets call it "anticlimactic".

Also LOL at server blacklisting over LB trolling in a dungeon.... these people need to get a grip on reality.