In the Balkans, the mother is sacred to a son, and unless you're ready to throw down, you don't go there. Some will just give you a punch or a pimp-slap to cool you down if you're friends, some are ready to kill you for it though. And weirdly, between brothers and the very best of friends, once you get to the level of jokingly insulting another guys mother or sister without him grabbing your throat, you know you've made a friend for life.