Christopher the whole idea of "professionalism" in dress or appearance is a widely-held superstition. The only important part of professionalism, the part that actually effects whether or not things get done efficiently and ethically is doing your job or study the right way. Except in jobs where one's clothing actually improves or hurts one's ability to get something done or to do the job safely (bullet-proof vests for example) it's irrelevant and it actually harms society when people are excluded from things for those reasons since the most capable person for performing the task might not get the job. Of course if I was trying to get a job I would try to look 'professional' as far as what others think is professional but off work I'll do what I can to combat this superstition and if I ever actually became the boss I'd throw out any rules I could based on superstition those ones included. I've heard Google only requires its workers to wear clothes. That's the dress code. They got the right idea.

However, I can see how in this case it is actually relevant, since if you wear something that a gang uses even if you're not in a gang you might be mistaken for it by that gang's rivals and attacked so it's more than superstition in this case. Still they should've let the kid know and instead of suspending him send him home, tell him the reason, and to fix it (difference is in the school record).