I understand it is hot in Thailand and I really think your beer belly look really sexy (NOT). But really would you in your home town walk around no shorts when you were visiting a government or police office?
I think the police in the UK would put a shirt on you if you walked in there with flip flops and shorts.
The same goes for Thailand, it is a normal country even if its your holiday destination and even Pattaya has a Mayor and a government officials.
Thai people take really offense when you can not dress even with a t-shirt when you go out. No they won’t tell you in the face because it is not nice in Thai culture but they will talk behind your back. So next time you take for example a are taking a driving license where a shirt and long pants, your driving licens can depend on it.