In Britain this is called a vodka jelly.
The reason it's so dangerous, is that the only alcohol you taste is the outside surface of the jelly (assuming you don't chew), the rest of the alcohol being safely tucked up inside the jelly until it melts in your stomach. Be careful!

It's harder than you think to make - the alcohol in the vodka interferes with the setting of the gelatin, and the heat from dissolving the jelly evapourates the alcohol. I recommend the following method:

- Take twice the normal amount of jelly you'd normally use1, and drop into your container of choice
- Nuke until you have a bubbling sticky mass
- Top up to half with cold water 2
- Fill up the rest with cheap vodka, rum, everclear, etc.
- Cover with cling film, and bung in the fridge for a few hours

1 - This ensures there is enough gelatin to set properly. I recommend lime :)
2 - This keeps the teperature down for the next step - nuking it heats only the jelly3, and then the water immediately cools it down again. If you were to use hot water to dissolve the jelly, all your alcohol would boil off.
3 - Microwaves directly heat water, fats and sugars. Make very sure it isn't sugar-free jelly, or you may blow up your microwave by running it with no load!

If you're feeling very showy, make a rainbow jelly by laying down thin layers, and leaving each colour to set before adding the next one. Be adventurous, and add different spirits to each layer! You can also make jell-o shots using the same method - drop a square of jelly into a shot glass, nuke, and fill to the brim with vodka. These can be made in bulk by nuking as many as fit in the microwave.

Have fun!