My buddies back in high school used to take the electric lighter component out of electric lighters (Like a normal pocket lighter, but it uses some sort of electricity to create a spark, rather than flint) and use those to shock people. I suppose it was one of those dumb pranks. The shock was more along the lines of a good static shock.
Thinking about it, it probably wasn't the wisest of things to do. I'm not sure how all of the electrical impulses work inside of the body, but I imagine that such a shock can interrupt these impulses. If you catch someone who has epilepsy or something, you may end up giving them a really bad day. Again, I'm not a doctor, but something like that can't be good for someone, even if it is a little spark.
I'm sure that shockers would be mass produced on the "prank" market and sold commercially if there wasn't some sort of danger behind the task. The reasoning behind that makes me wonder that there is a good reason behind not producing such a product.
I'm not trying to be a downer or anything, but in reality, the potential to hurt someone is pretty good.