I think it's just like any other fetish. It could be something inanimate like a piece of clothing - gloves, socks, shoes/boots underwear which represents something masculine. It could also be a trait like the way a guy walks, his persona like being cocky, the way he speaks and carries hiimself, etc. - all these could be a turn on under the right circumstances. Heck we're all here because of a fetish of finding dead guys hot and exciting. For me, feet are hot as well, but not as hot as a well worn pair of boots or sneakers worn on a hot masculine fit dude.