A quick glimpse of underwear?

Ok, there is this guy. Older man, 72, married, three kids, just retied from a delivery route. Could not be straighter. But this is not about that. With a couple of guys, we eat lunch together several times a week. Often he stands up or reaches upward (ok, I’m watching his ass) his shirt might ride up a bit or his pants had ridden down a bit and I’m there looking at a quick glimpse of Joe Boxer briefs which aren’t brief at all or white y-fronts with a blue horizontal tripe. Just a tiny glimpse of a bit of blonde hairless back skin. For me it is a huge turn-on. Just a bit of skin showing. Today we went doing some community chores and he drove and I was Shotgun and every time he got out I was peeping, did see some skin. Made me think for some time, if not always, I have been turned on by seeing a bit of accidental exposure. Anyone else like this? He is totally unaware of any of it.