*shrug* Whether it's playing a single character or 5-boxing, I give the same response to everything, unless I'm feeling charitable:

Warrior: priest fort plz
Me: NI HAO MA
Warrior: what r u chinese?
Me: NI HAO MA

or

Shaman: Hey lol u r botting, rite? u r not 5 ppl?
Me: NI HAO MA
Shaman: lol u r farm botting omfg lol reported
Me: NI HAO MA?

Either case, the first guy just ignores me, the second actually did report me but the GM cleared things up with me being a multiboxer and everything was fine.

Moral: Always respond with a Chinese greeting and everything will be okay. =D