If you are not a resident (i.e. you are on a tourist visa or exemption of visa), you only need your national driving permit to be able to drive in Thailand. So, if you are visiting Thailand as a tourist and you want to rent a car for just a few days, you just need to carry the driving permit you obtained in your home country. This is clearly indicated in the Motor Vehicle Act:
In case there’s a treaty between the Thai government and a foreign government regarding mutual acceptance of driver’s license, an alien who doesn’t have an immigrant visa may drive a motor vehicle with a driver’s license issued by such a foreign government, or an automobile association authorized by such a foreign government.
International driving permit (IDP) is the preferred license as I’ve been stopped at a check point and my license was taken until I paid a 500฿ fine.
Yes they do have there own way of driving, to include more then two riders on a motorbike or scooter. You will see pickup trucks loaded way past there safety limits as this is the only means too travel.