This is actually one of the things it took me the longest to get used to when living in Asia. You don't have to be scared of the police here.
Back in the West, if a cop starts chatting you up, you immediately stand up straight and begin thinking, "oh shit, what did I do wrong?" type of thing. Whereas here, it's the complete opposite. Your average cop is just a good guy, happy to chat you up, laugh and joke around with you a bit, etc. "hey, so what did you buy? oh, you got some beer! good, good, hope you have a good night!", all the while with a smile and wave.
They'll have no problem putting you in a cell if you cross the law, and although I've never been, I'm pretty sure I don't want to experience the inside of a Thai jail cell. For all intents and purposes though, cops here are friendly as hell. That one took a bit of getting used to. Little different than the power-hungry boys of the West.