Frankly chess players on the whole are a sloppily attired bunch. Noted in a previous thread also at the body odour issues of certain players.
Remember a friend telling of an English GM who missed the flight to the great relief of peers as he hadnt washed for so long.
Uniforms are for teams. Chessplayers mostly compete as individuals.
There shouldnt need to be rules, but sadly many seemingly 'clever' people have no idea how to behave or dress. Mind you, same in any office I guess.
I remember the Calvia 04 prizegiving - the Japanese team on stage all wel besuited (we were top of the bottom - category E. yay!

). A leading Russian super-Gm in crumpled too-big grey suit, plus dirty white trainers standing just in front. Oh, no. Please. An insult to sponsors not to dress properly for a prizegiving.
So - yeah, should be rules.
Or prizes could partly consist of:
Vouchers for clothing shops
Soap and shampoo.
A year's subscription to GQ.
And a good telling-off for their mums who should tell them about such things.
PS
toyomi:
ano, ... nihonjin desu ka?