The same is true in Australia. While you can wear speedos, it's something of an unwritten rule that you shouldn't do it unless you're good looking. One of Australia's (many) ex Prime Ministers was widely derided for always wearing "budgie smugglers".

There was a TV ad in Australia (originally from the UK) related to this. It asks the simple question: "How far away from the beach do bathers become undies?"

https://www.youtube.com/watch?v=Brg_zHXIHC8