One distinct possibility is that if you aren't careful about how you dress, people will think that you are walking around with a persistent hard-on.
When at univ. I used to wear much closer fitting trousers than I do now, and several of my fellow students came to precisely that conclusion. I didn't discover that this was common gossip until a lot later.
In changing rooms etc. the odd double-take is inevitable. People will also stare, but usually they try to be subtle about it.
My landlady in my last year at univ walked in on me once without knocking and got an eyeful; for what seemd like about 30 seconds she stood there staring like a rabbit hypnotised by a snake. And yes, she did treat me very differently afterwards (she got nervous and giggly around me, and couldn't do enough for me); but she was nearing 70 at the time.
Not quite the sort of story you want I imagine, but it still makes me smile.