We went on a class trip to Thailand a bit over a year ago during sunkran (i probably spelled it wrong) and before we arrived we were taught some laws to look out for.
1. Don't touch peoples heads, especially children. Something to do with it being insulting or something like that
2. Don't go toppless, this rule applies particulary to those with body tattoos because they would look like gang members.
3. Do not make fun of the king, or of any place depicting his face.