Unfortunately, these sort of totally stupid situations are pretty much par-for-the-course when driving here. You need to be very careful when driving around because getting into an impact/altercation with any other vehicle/person can be problematic on a few fronts.
Firstly, the way the insurance works, as most people (if they have it at all) just get the cheap one that pays for someone else's vehicle if it turns out to be your fault... problem is that you need a dash cam to even have any hope of getting it straight with the local cop that it wasn't your fault. Also, many Thais don't bother with it so the cop might side with them to help them out and get your insurance to pay for stuff.
Secondly, anyone driving like a moron you should just let them speed past you and get out of the way... the hidden benefit to this is that if the cops are up ahead on the road doing a check, then they will be busy dealing with the moron when you arrive, and it's not a race track even if certain sections of the moron locals think it is.
Thirdly, don't get angry or show road rage, even using your horn and annoy some of them, just employ your emotional intelligence and pass it off... lots of Thais carry weapons in their cars and can act like 12 year-old-boys in the playground.
Also, make sure you are completely legal, like with license, tax, copy of blue car book info, insurance et al or they will use it against you if anything goes wrong.
The type of driving from the locals I really dislike is the habbit that motorbikes have of just joining a road from the side and not looking or even stopping, just drive out and expect you to miss them... often committed by older Thais that still think a highway is the same as the village.
To be honest, getting into a crash or altercation on the roads can be one of the worst possible things you can get involved in here, as it can have drastic consequences... much caution is advised to all that drive here.