To be honest, it depends on the pools.
Some forbid thongs, some authorize thongs and most of them do not have precise rules and may tolerate or may forbid thongs.
What there is to know :
- gender discrimination is forbidden. So, if thongs are authorized for women, it is OK for men too.
- Read the rules or observe if there are women with thongs.
- only conservative thongs are authorized / tolerated. Mesh, see through, G-string are always forbidden
- Avoid busy hours during summer because there is a lot of rednecks
I think over half of the pools authorize or tolerate thongs for men.
Since last year, I went to 10 differents pools. No issue.
Each year, I see english men to be rejected because they wear boardshort.
It is priceless to see their face when they see me and they understand that thongs are OK and boardshorts are forbidden.