@Neushaartje
Sure, in reality, but in manga, you can use the trope for ecchi and comedy purposes. Girl cumming = hot. Guy getting probed and hating it = funny.
Plus, unless a guy is receptive to it, the repulsion will likely override the pleasure aspect. In addition, you kinda have to train yourself to feel pleasure that way, otherwise you'd have men jizzing every time they took a shit.