See I disagree

The Boss clearly saw the Leatherman's attire and thought him to have taken a wrong turn, knowing there was a leather club only two blocks from his territory, and was merely trying to set him on the right path

When Leatherman reacted aggressively, even going so far as to challenge the authority and experience behind his words with a flippant "fuck you", the Boss realized he needed to set this guy straight, not just for his own honor, but for the good of society

So, he challenges Leatherman to an honorable duel, clearly stating the terms and ruleset to ensure no unfairness or misunderstandings, like any proper authority figure

The Boss of the Gym's a role model, bro