1) Tell them nicely to do something right.

If you get a rude reply:
If you're a DPS, take off all equips, except weapon. When asked why, tell them it makes you more aerodynamic.
If you're a Healer, take off all equips except weapon. When asked why, tell them it helps you bond with the spirits better.

That usually shuts all those "I play the way I want people up nicely".