Pretty much any situation that would enlist the use of any type of alcohol, usually rum, vodka, tequila or in extreme cases (if your trying to kill something) even grain alcohol. The alcohol is used to substitute some of the water or fruit juice used to solidify the jello shot mix.

An American mathematician by the name of Tom Lehrer is thought to have been the 1st to craft the jello shot in the near beginning 1950s while working for the NSA, where he developed vodka jello, this was his genius idea to sneak alcohol onto the military base with out any of the commanding officers getting wind to it.

The highest alcohol content is somewhere in between 18 & 21 oz. of vodka per 3 oz. package of Jell-O powder, or about 30% (ABV) alcohol by volume.

Alternatives

A few gelatinous desserts can be manufactured using agar instead of jello, allowing them to set far quicker and at higher temperatures. Agar, a vegetable by product made from seaweed and is used especially in jello shot powder mix for an accelerated setting time and Asian jello desserts, but also as a substitute that is acceptable to vegans and vegetarians. Agar is far more closely related to pectin and a few other gelling plant carbohydrates than to ordinary gelatin.

There is one other vegetarian choice to gelatin, it is called carrageenan. This alternative how ever sets harder than agar and is often used in kosher style cooking. Though it, too, is a type of seaweed, it does not have the same bad sort of smell when being cooked that you would sometimes find when you cook with agar Chemistry

Fresh pineapple should really be avoided when making jello shots, it contains the enzyme bromelain which must can never be allowed to mix with the jello shot mixture as this enzyme will prevent the jello from setting, this enzyme is common in most citrus and tropical fruits. Papaya and pawpaw contain the enzyme papain, kiwi fruit contains actinidin, and figs contain ficin- all with similar effects. Cooking denatures the enzyme, rendering it inoperative so if you want these jello shot flavors get the wife to fire up the stove.