I wouldn't resort to violence, but would put someone like that in their place real quickly by letting them know I'm a grown ass man, in a free country and it is my choice to be with whomever I want and it is not the concern or business of any outsider to be rude and insert themselves into the affairs of two consenting adults in 2011.
So they ought to sit down and worry about their own personal lives and not the lives of someone else that they they don't know anything about.
I may toss in a few expletives as well in the heat of the moment, but the point will get across.
Of course bigots are usually more subtle than that, because they know better than to open their mouths in a public setting. That is why you can't take bigots seriously, they can often be the biggest duplicitous, two faced cowards. They'll be smiling at you outwardly or profess how many this and that friends they have and on the inside hate you.
Ironically it was a couple of white guys that spoke up vocally to the two black females and the white guy and white female about the BM/WF couple, the black couple seemed to be more laid back about them being criticized by the two black women.