That's a matter of context, and raises the question of whether they're in a civil society or a war (or both at once). In principle in a civil society nobody should be punching anybody in the face and mitigating circumstances like the other person being a nazi are only details. But see Sartre's feelings about living alongside nazis in occupied France: the were very polite and pleasant, and the whole situation was tense and awkward because you're unsure of your duty in that situation - is it war or not?