This used to happen in wow, its real easy to avoid..
just don't use aoe, when you see these flagged idoits coming on you, stop using aoe and just use single target attacks. it may make the battle longer but you won't flag. also rember to use the tab key to select targets when the idiots are around, that way you don't acdiently click on one of them and flag yourself.
when the battles done feel free to give them the finger and get on an alt and laugh at them. that way they know what special children they are and how you won't fall for there fail wow tricks.