Not an AIBU cos really the title says it all. At massive local pool with group of five girls aged 10/11. Luckily they were showering in different area, I was waiting at lockers for them to come back and get changed. Bloke in the shower, nonchalantly steps out of his trunks and made big show of rinsing them out. I did a double take, then the slow burn whilst my brain tried to process what i was seeing 
. I nabbed a passing lifeguard and said "look!!!!" He was (after getting dressed) frogmarched out and told if he came back in they'd get police involved. Creep. My group of girls saw nothing but that was more luck than anything. shudders