90: Flashing headlights.
Only flash your headlights to let other road users know that you are there. Do not flash your headlights in an attempt to intimidate other road users. Or to let them know you do not approve of their safe overtaking maneuver just because you are a lifeless turnip without the skill to do so.
They flash me, I flash them back in case they haven't seen me and if they shake their fist at me I wave back with a big smile. (maybe this doesn't help but it makes me feel better)