This is a tough call because Thailand has a few snakes that could kill you within a couple hours if you weren’t able to reach medical care quickly enough.
I think the King Cobra, if it got a good bite on you – would be the worst snake to be bitten by in the country. I have a friend who lost his little brother (adult brother) to a King bite on the shoulder that killed him in less than ten minutes. Luke Yeomans from the United Kingdom, all set to open up the King Cobra Sanctuary to the public was bitten and died within minutes as he had a massive coronary.
If you are allergic to the venom of the snake that bites you, death could come very quickly. Some snake experts recommend carrying around a Ventolin inhaler that people use for asthma treatment. If bitten by a venomous snake in Thailand you may start losing your breath. That’s when to take a spray. Others insist on using epi-pens at the first sign of anaphylactic shock.
I always have the ventolin inhaler – I am slightly asthmatic so, in this case it’s actually a good thing.
More info about King Cobras here.