You would lose 1/3 of your eval at States if you let this happen as an umpire in Florida (which means no States next year for a start). Frankly, I don't care what happened in the past, nor do I care who you are (or think you are), this is what is happening THIS game.
ART. 3 . . . Any time a coach is in live-ball area to confer with players or an umpire, or to occupy a coach's box, the coach shall be attired in school uniform or jersey/coaching shirt with coaching shorts/slacks or warm-up suits (including fleece warm-ups) in school colors or colors of khaki, black, white or gray. Cut-offs or any type of jeans are prohibited. Jackets are not considered part of the coach's uniform.
PENALTY: (Art. 3) A coach not dressed in appropriate attire shall not be permitted in the field of play following the pregame conference for the duration of the game or until the situation has been remedied.
So yes, there is a 'no jeans rules' in NFHS.
USSSA has a rule that requires a cap must be worn bill-forward
.... and so on.
These rules exist because (like a lot of rules) people can't be trusted to automatically do what is appropriate and apparently need to be told. Such as this guy apparently.
Soooo... What you're saying is that jeans are a no-go, but a velour track suit might be acceptable, in team colors of course course. Bada-bing!