Originally Posted by username79
This works. "Who are you??" is also effective in mixed company.
I disagree. "Who are you" lacks punch screw the sensitivities of the rest of them. Said properly, with a combination of mischief, roguish charm and feigned malice, 'Who the fuck are you?' is at once disarming, intriguing and can't be ignored.
It works even better when you say it to a third party as in "And who the fuck is this?"