The answer to your last question: no, we don't realize. Our junk sheds. The little man sprigs just leap off our unmentionables, and crawl around like inch worms.
He is your roommate. So talk to him like a roommate. No need to bring gender into this. And keep in mind: he will reflect your behavior in this regard. The way you deal with his testicle fluff is the way he will deal with, I don't know, tampons in the trash bin. Some guys don't even like to SEE those things.
And how would you want him to talk to you about an uncomfortable bathroom habit? As directly as possible. Be straight up with him. "Dude, clean your pube curls off the poo throne." Or "Hey, valued roommate? I'm going to need you to sweep up crotch springs in the bathroom, okay?"
The guy probably doesn't even realize it's happening. It's like farting. Most people are pretty much immune to their own stink. These unsightly body hairs are probably invisible to a guy who has OBVIOUSLY never lived with a woman.
Just bring it up. No big deal. Make him aware of something he's not aware of. That should take care of that.
Ewwie. :S
Lol I have two brothers and literally all the time this happened when I lived at home.