Or you can respond to them with my old stand-by:
F**k you, you @$$40l3!
If the want more, I’ll ask them if they are willing to bleed for their cause.
Sums up the best response I’ve seen.
Or you could just look at them and calmly ask with some derision in your voice, “so, what are you going to do about it?”
Then watch them either fly off the handle or withdraw because they can’t do a damn thing about it.