Wearing underwear with swimwear kind of defeats the point. Especially with speedos. As many have observed, underwear under swimwear/shorts never dries out properly, and swimwear is designed to dry fast. When I was younger and living in Australia, board shorts were my uniform in summer. If I was just wearing them as casual shorts, I’d usually wear briefs underneath. But if I were swimming in boarded, I’d take of the briefs. But it was perfectly acceptable to go commando in boardshorts even if just wearing them for daily life. They’re designed for it.