Never heard of toy stun guns, but I'm another person who enjoys or at least doesn't mind the sensation of mild to moderate electric currents. Electric cattle fences are too big a jolt for me, but I accidentally zapped my hand with some 240VAC a couple of weeks ago while working on a broken water pump, and the shock was just about at the upper threshold of what I could take without too much discomfort, however I've no idea what the amperage was, since it depends on how conductive my skin was at the time and how good the contact was. If I used electrode pads and conductive gel with 240V AC, it would be a different story.
I've got a circular scar on my right arm that looks like a cigarette burn, which I got while experimenting with passing electric currents through my brain. I was using 20mA at 24VDC, which produced a barely noticeable tingle/itch, but I left the electrodes on for too long on one of my attempts, and when I removed them, there was a purple circle where the cells had been killed through the full thickness of the skin on my arm, and some smaller marks on my forehead from milder burns. The burn on my arm turned into a pit with a scabby bottom and sides when my phagocytes removed the necrotic tissue, and the skin slowly regrew from the edges over the course of the next couple of months.