This is a collage of me and some of my underwear and swimwear, although some was not mine. It might seem weird, but I do enjoy putting on other people's underwear and snapping a picture, because I don't need to own it, I just want to know how I look in it. It started with brief to boxer brief, then slowly expanded into jockstrap, thong and other peculiar underwear article.
I think all gay men like to see other men in underwear, but whether it would add to the intensity of his sexual encounters is what differentiate those with underwear fetish and those not. If it's just a pleasant sight before you rip it off and remain naked till the end, you probably don't have underwear fetish. But if you get a kick out of having an underwear on most of the time during the session, then it's likely you do have underwear fetish. But then again, fetish is very personal, it doesn't matter what other people thinks, as long as you yourself like it. Just like being gay.