As a guy, the ones I find most irritating are when the seat doesn't go back on enough of an angle when left up so falls down when trying to use it from a standing position (though the way some guys aim, they are better off sitting anyway).
@tRicky I think this is a case of "too much detail"
Rachel's right though, there are many public toilets where it's difficult for even a medium-build person to get past the cubicle door when opening it in order to emerge.