Well my friends were not aware that dress shorts were prohibited. Maybe they should post it on large signs in the lobby and elsewhere.

Certain rules are stupid, and that is one of them. That is not a HIGH standard - it is an arbitrary one, as shorts are not inherently less dressy than long pants. A pair of tattered jeans is quite a bit less appropriate than a pair of crisp Bermuda shorts - the shorts also being a vastly more intelligent choice in 98 degree, 98% humidity that typifies Bangkok. Anyone who would choose to wear long pants in that type of climate just to observe some Victorian-era concept of propriety is, quite simply, a fool.

On a positive note, there are several far better hotels in that part of Bangkok that do not get hung up on that sort of stupidity that pervades the Mandarin Oriental - and smart folks will obviously choose one of those superior choices in hospitality and leave the Mandarin Oriental to those folks who's tastes are stuck in the 19th century. Quite simply, the vast majority of folks who feel that this sort of dress code is apropos will be dead within a couple of decades, and with them, the business establishments that cater to that obsolete concept and fail to adapt will surely follow.