Street food or any hole in the wall Thai restaurant are perfect (a particular favorite dish of mine is Tom Yam Kung or Tom Yam Moo). If you want to ruin KFC for yourself (forever) try Thai Fried Chicken off a food cart. The mushroom and pork sausage is to die for, especially with some green chilis. If I go on talking about Thai food this will be 10000 words long so I'll stop myself here. Curries and Pad Thai are a very small part or what Thais really eat.

As for local culture go to Pattaya and hope you have the willpower to leave at some point.