One thing I can tell for sure is that this thing would have to be battery powered for safety reasons.
Police tasers operate off of small batteries and once in awhile someone dies.
Electric fences that are used to keep cattle out (or in) tend to work at voltages like 10-20kV, give you a good shock, but are basically considered safe to humans due to the very low current they can produce. One of such devices may be a suitable starting point. They're kept safe by limiting both the maximum current and the duration of the shock.
Other devices that are designed to deliver safe electric stimulation (as safe as it can ever be, of course) can be found in the sex shops. Such electrical sex toys are generally advised to be used below the mid riff only. Nipple to nipple while obviously attractive is a risky idea, as the heart is right in between.
One thing I would NEVER do is attempt to build such a device myself. A minor mistake and your party gag turns deadly. You would also need very good testing equipment to make sure the currents and shock duration are what you expect.
I have a defibrillator implanted. zap me and you risk damage to my obscenely expensive implant. I will express robust displeasure, vigorously.
Police tasers operate off of small batteries and once in awhile someone dies. Of course, your little circuit isn't supposed to as strong as a taser, but...
early models ran off of regular 9v, now they've got a proprietary rechargeable thing
.......... but I think having someone knowledgeable advise me on things I should be watching out for would go a long way than me going at it by myself.