A simpler solution is simply including exposure of one’s undergarments in the “indecent exposure” ordinance.
You condemn the majority of middle age plumbers.
IMO that would just result in lots of people not bothering to wear underwear. Pants would still hang down and it would be worse than it is now.
One thing that I have discovered over the years is that you have to be very, very specific with people or you get a lot of “Well, why didn’t you say that in the first place” comments. There is no accounting for taste, class or common sense.