What are the rules for fights?

i know fighting is not the best solution. but sometimes it happens. what i want to know is what is allowed and when. like, if it were just defending my honor in a bar i wouldn't choke a dude. but if i were defending my girlfriend from getting raped i would kick in the balls and gouge someone's eye out. what is the etiquette for fights? when is kicking allowed, choking allowed, slamming head on concrete, kick in genitals, eye gouging, etc.. .. .. .