I work in a small software company of around 10 people. We are all very "informal" with each other and there is no dress code or anything. It's a very laid back company at the moment and I'm fine with that.
The co-worker in question is an older male in his mid-thirties, who is a bit on the heavy side. He dresses in a way that avoids belts, which means that I often see plumber's crack when I look his direction, even when he's just standing or walking.
He's overall a very nice person to work with, which is what makes it more difficult for me to tell him that it really bothers me. There have been a couple particularly revealing incidents where I almost stopped him to talk in private, but I never did it.
He seems completely oblivious to his constant half-mooning, making me wonder if anyone has ever said anything to him about it, which is why I hesitated. It seems like he's not aware of it at all, though I don't understand how one could not be. I'm overweight myself, but I wear a belt and I usually notice if my crack is showing and avoid it.
I have no idea how to tell him about this in the nicest and least offending way possible and I'm afraid I'll taint myself in his eyes forever if I told him about something so embarrassing.
So, how should I tell him that he's exposing himself, and that it really bothers me?