Why cant underwear be worn with out pants overtop no different then bathing suits

The rule of thumb is if you are wearing speedos within 50 yards of the water they are considered to be speedos and therefor “acceptable” as swim wear. If you are wearing speedos more than 50 yards from the water they are considered to be underwear and therefore not suitable for public view.

In NZ and OZ there is a rule of thumb saying of “undies undies togs” which is normally used to distinguish between close enough to the water and not close enough to be considered swim wear. You decide.

Sometimes it is hard to tell the difference between mens underwear briefs and mens swimwear briefs.