Use a horn. Do not engage with people this unless only in accordance with the rules of the road and the law. They are looking for a reaction and potential mitigation in a court. If you have to dismount and walk, do so, ideally to an area with witnesses.
One guy once over-took me on a blind bend with cars either side. Tried to grab me as I attempted to go round. In fear for my person I hit him. I did not want to. It didn't make me feel proud, but I had no other choice. Later on the police arrived and paid him a visit to where he worked (he grabbed me nearby). No action taken against me because as mentioned I didn't get into any kind of argument with him, I tried to fee and had no other choice. He was also lucky I didn't do worse, as many people would.
What I'm trying to say is, don't engage. Observe but not absorb where possible. At least then you know you've covered yourself in the eyes of the law should some crazy bastard try to assault you or worse.. yes, it could be life or death. If you reach that point then there's no rules but reach that point only after you have exhausted all other avenues.
I say all the above irrespective of your mode of transport.
GU59YHZ or GU69YHZ?