Magindat is correct, in his observation...
The way I found to be effective against starting a war (retaliation), is to allow that person to keep thier dignity...
Don't stomp this person into the ground...this will humiliate this person...increasing the chance of retaliation...
Rather, simply let that person know "WE ALL KNOW" who they are, and politely ask them to remove themselves from this family...
This is important: Wish them well on their way out...After all, life must be difficult for this person...If not now, sure will be once he/she is identified...
Wow, did I just write this? The things you learn as you get older...Just a few years back, and my response would have been just the opposite...
But I have come to learn, that whenever I beat the sh$t out of someone (was a bouncer at various night clubs for @ 13 years, so this would happen @ once or twice a week)...I would pick them up, dust them off, and even help them with their wounds (even called the ambulance for a few)...Told them sorry I had to do it to them, shook their hand, and politely asked them NOT to bother me again...They never came back...
The one's I stomped into the ground and spit on as I walked away, often came back; Requiring me to do it all over again to him and his friends...This got old as I got old...Now I let them keep their dignity...and all is good..
Good Luck...
ALOHA