Phuket and Bangkok are the most likely locations you will be pulled over riding a motorbike.
Phuket is famous for pulling over foreigners that are not wearing a helmet, do not have a proper license or insurance. The fine can average 500 to 1,000 thb.
Bangkok creates check-points in busy areas so they can stop as many motorbikes as possible.
In these situations it is better to just pay the fine and if you are not legal, avoid them in the future.
Since these fines are collected in cash, there is speculation of massive corruption with this money.