I'm not sure if I'm biased. This is my observation. In Thailand if you get to see girls wear "very short denim shorts", more often than not they're either WLs or Gogo Bar girls etc. The decent ones studying in good universities or the Thai-Chinese girls with rich papa mama selling gold or shark fins in Yaowarat don't subscribe to the same dress code you mentioned.
Sawasdee Krup Khun Pojaman.
Last night I quiet because too much drinks and food until get back to hotel pengsan liao. Will be back this evening.
Since you asked I must say your observation is a little biased KYP please allow me to share. WLs and Agogo girls and Cayote girls view themselves lower than "proper" girls. Yes they are aware of this themselves. If you ask them if they had been to Siam Square, Paragon or Emporium the answer is obvious, many not been there and when asked why the answer is simply, its too expensive. Yes prices may be alittle too expensive there compare to night markets like in Ramkhamhaeng or Huay Kwang night markets (their favourite hand out places) the other reasons are, they feel shy to shop there because they feel they banook and also they simply have no time as the only time they have is after work which is after midnight.
So when one goes to Siam Square, Paragon, Emporium one can see many beautiful and young girl there wearing short denims and I will say most are just normal young girls but whether decent or not really cannot tell. Talking a little bit more about denim shorts, I have shopped for this with some ladies before and I must say that a new arrival denim shorts in Siam Square shop could cost around 2000baht (no brand or just brand of shop) and if one can wait for 1-2 months and shop at say normal night markets I mentioned price for the same shorts could be had for less than 800 baht. Brand-less or unknown brands clothes in Bangkok can be expensive if its just arrived and sold in Siam Square or even Ratchayothin Major night market.
Side track a little recently I was with a nice Thai Chinese man around late forties. Has beautiful Thai Chinese wife (not the hi-so ones). I was drinking with him and just talking about Thailand ladies. I said to him how lucky Thai men are because Thai ladies are so caring and considerate to their husbands and family. He told me not true for Thai Chinese ladies because afterall they are still Chinese in their upbringing for any Chinese family. He said what I am talking about are the real Thais and Thai Thai ladies. He told me that Thai Chinese ladies and even men are afterall still Chinese because of upbringing whether rich or poor.