Basically its an instance when out and about usually in a totally unexpected setting or scenario where you may see or hear something that is SO mentally arousing to the point it shocks you how erotic it is that the primal instinct side of your man-being lets out a sort of almost caveman sounding murmer or lowkey moan like "uuuHHHHHH!!" in a shock face as an erection builds up in record time (bear in mind I don't mean cumming sound)
Any guys here experienced such a thing? its seemingly involuntary.