I think I get it. It's the permanence, isn't it? I'm an amputation fan, so I know how this stuff works.

Once a cock is cut off, there's no going back. Whenever the man becomes horny, he'll reach down to jack off and there's nothing there. No more jerking off, no more sticking it in women. His mind will flash back to that time, the last orgasm where you cut off his cock. His mind flooded with desire, yet no way to satisfy it, he'll think of you, longing to relive that once in a lifetime experience and achieve the release he so desperately needs.


Yeah, that's probably it. Either that or you find the intense crescendo of orgasm becomes even more intense when it is so final and horrific. All that pressure and build up, his need to cum clashing with his terror, knowing that the closer to orgasm he gets, the sooner his life of sexual pleasure ends. He'll fight himself, wishing never to cum, but at the same time he cannot fight his primal urges, the all-consuming obsession with cumming. In the end, had cannot hold back and he releases his final load, spraying his seed as your knife goes snip-snap lopping the instrument off and putting an end to his means of release. He'll cry for his loss, but he'll thank you too, thank you for the pleasure the likes of which he could never imagine, the bliss and mindblowing sensation of the one-last-orgasm. Still twitching in your hand, the severed cock slowly loses what life still remains in it, until at last the blood drains and it shrivels up, never to grow hard again.

Maybe something like that?