Thai police, viewed negatively by some, are in general pretty
nice and friendly. The main thing to keep in mind when dealing with
police is to be polite and respectful.
If you know some Thai, make sure to sprinkle lots of polite sentence
endings into your speech. If you don't know any Thai, keep your voice
down, smile (don't smirk) and use simple English words that will probably
be understood,
for example: "I'm sorry", "I don't know", "Please help me."
Some foreigners think they are singled out because they are foreigners.
Some Thais think foreigners get away with a lot because they are
foreigners. The truth probably shades over toward what the Thais
think.
First, most police don't speak English too well and don't
want to deal with explaining something to someone who doesn't
speak Thai.
Second, most Thais are concerned about the image of Thailand, and
even if someone has done something wrong, like running a stop sign,
the police will frequently let foreigners off with a warning.
Another important thing to keep in mind is to remain calm. Getting
agitated will do no good whatsoever. This is especially true if you
have to go to the police station. This can happen, for example, if
you have a fender bender with another car and can't agree on
whose fault it is.