Express negative opinions about the King or any member of the Royal Family. Thai people have utmost respect for the Thai monarchy.
Pass anything with your left hand and point with one finger.
Get involved in anyway with drugs. Penalties are very severe from 10 years up to the death penalty for trafficking.
Point at people or things with your feet.
Touch a Thai person on the head.
Raise your voice or get angry as it is a sign of disrespect in Thailand.