When is it “okay” to physically fight someone?

So today I was chilling driving minding my own business, and as I am about to leave the gas station a lady turned in super fast and almost hit me.. now she didn’t see me there because a car was blocking her view but if a car is blocking your view why would you turn in fast as hell? 😂😂 so anyway I shook my head as if saying “seriously?” But no words came out of my mouth (I am 25 weeks pregnant and I wouldn’t start a fight with a stranger) but anyways as I drove past her she lowered her window and said something along the lines of “Don’t get beat up!” As if saying she was gonna get out the car and fight me and I honestly just laughed and drove away because really?? How old are you? 😂😂 Anywho that made me wonder how many people in the world are actually willing to physically fight someone over something as small as that?? Under what circumstances do you deem reasonable to actually fist fight someone?