"Appropriate" Swimwear

[Torchwatch]

2" sided classic racing Speedos (and other similar briefs) are suitable swimming attire in any sports environment.
Even a 1" side isn't inappropriate but you may be pushing the envelope.
Going towards a low cut brief that allows a tunnel view at the rear may be going too far, while wearing a swim thong would be asking to be thrown out.

A tenant of the British law on indecency was whether public opinion regarded material to be indecent, by pleading not guilty the matter would be taken before a jury and they would decide. The resulting trials eg that of Lady Chatterley's Lover or Oz changed society.

The thing to do is to wear 2" or 3" Speedos and see the reaction, if the majority (or even a significant minority) start wearing speedos then you could aim for something more adventurous. Remember, a frog will jump out if placed in a pan of hot water but sit happily until he is cooked if placed in cool water and slowly warmed.