This sums it up. There is no simple line you can and cannot cross, every case is judged on its merits and what the people involved - assailant, victim, police, judge, jury, etc - think is reasonable. Sometimes they misjudge the situation, sometimes we think they misjudged the situation. Recall that one of Jeffrey Dahmer’s (14-year-old) victims was returned to him by the police, who thought it was just a BDSM game or argument.
So whatever you do, you proceed at your peril. You cannot contract away the right of the state to prosecute anything it deems appropriate. the only question is whether the system will deem your actions criminal in the context.
If I were followed around the bar by some guy saying “Go ahead, punch my nose” I would assume that this is a prelude to him then having a (in his mind) valid excuse to retaliate, and so any assault would instead be self-defense. The only point of contention would be “why didn’t you just leave?” and the logical response “because then he would have followed me outside where there were no witnesses.”
There have been a decent number of assault cases where the one participant says “but I thought she liked it rough”, while obviously she didn’t like it that rough. You proceed at our own risk, both physically and legally.
Perhaps the more interesting example is ice hockey, where the rules are clear on what is not allowed in physical contact - but there are “unwritten rules” that players will engage in fistfights at times. The presumption in playing the game is that the players consent to the sort of behaviour “tolerated” by the league and the overall association. However, there are certain behaviours that are explicitly not tolerated. The player risks ejection, or bans from several games to lifetime, if they violate these - including assaulting the refs, using the hockey stick as a weapon, assorted dirty maneuvers intended to significantly injure, etc.
A recent trivia show pointed out that MMA forbids hair-pulling; certainly this is not the “anything goes” of a bar fight with or without knives, it’s more like a dance with pain. Most of these sorts of sports seek to avoid deliberate serious long-term injuries as opposed to inflicting assorted levels of physical pain, and have a means to “yield” or signal an end to further consent. (It seems to me boxing like some other sports was until recently simply oblivious to the longer-term damage implied in head blows.)