Achmed's students wouldn't see him instantly and painlessly transit to paradise, and wouldn't be shouting "Praise allah, he's now enjoying his 72 virgins!"
They would watch him scream and moan, with the sure knowledge that he wouldn't be able to spend eternity raping his ever-virgins.
These are the people who wrap their tinkle toys in foil before donning a suicide vest, believing that this will protect them for the after life.
A life without sex, followed by an eternity without sex? Where's the up side?
Tulta Munille!
Bullet coated in pig grease.
100% irreversibly lethal, but on about an hour's time delay.
Only thing missing from your scenario is dipping the bullet in pig lard.