Don't try to shake hands with a monk. Don't drink the water. Don't forget insurance. Don't forget your international driving license. Don't change your money before you arrive. Don't overstay your visa. Don't assume Thailand is, in fact, the land of smiles, especially if you're a male, farang abuser.
I went through immigration 6 hours after the midnight deadline recently. I got an overstay stamp and a guy in that section told me he was being forced to leave the Kingdom - I didn't get the story though, but he looked in shock.
And it's not only a problem if one is detained. The ineradicable overstay stamp in the passport is the thing I'm always worried about. If the OP's never coming back to Thailand it's irrelevant I suppose.