Why is it guys get horny when I cry?

Why is it guys want to sleep with me when I cry? It's the weirdest thing. Friend, acquaintance, co-worker, boyfriend of friend, stranger... it doesn't seem to matter... they show no interest in me that way until something makes me sad, I cry and then *wham* they want me in the car-park, train-station, lounge room, bathroom... again it doesn't seem to matter. It's sick :( Heck, the only time a girls tried to make out with my was after I'd been crying! Why on earth would tears turn anyone on?