It has become fashionable, it seems, for young men to wear boxer shorts under their swimming trunks [Jul already commented on this].

I personally can't understand the fashion statement. I don't really want anyone to know that I wear underwear by Calvin Klein and Yve St.Laurent. But then, whoever has been able to understand the fashion statement of young people of any generation?
Hygienically speaking , however, the fact is that any amount of fabric worn in a swimming bath is unhygienic - the more you wear, the more dirt and bacteria is transported into the water. The 'problem' has become that serious, that Basel has already put up signs prohibiting underwear and Zurich and other cantons want to follow suit ...

Ed. The rest of this post has been removed.
Apparently it was causing trouble in other parts of the world.
Sadly no-one was prepared to tell me why, or how it may be altered so as not to cause offence.