One challenges another to a sword fight by posting at least 3 penis's (8====D) on random wall posts of a single person. He or she may fight back by posting 4 or more penis's on their wall (and so on). it is a battle to the death until one fighter can no longer one up the other fighter.
Steve is the master of facebook sword fight. he once posted 83 penis's on my wall until i gave in to his wrath.