I don't mean full on fetishes, but little things here and there that you wouldn't mind coming across more often?
Mine (well, one of them, I suppose) is fairly tame, but for some reason I just love seeing busty girls borrowing or playfully trying on clothes belonging to their lesser endowed friends. Aside from the whole "barely contained boobs spilling out" thing, something about a chuckling "well THIS clearly isn't going to work" or a slightly cocky "I think it's clear who the real winner is" expression just gets me going.
If any of that made sense, at least...
A few examples, albeit mild ones.