If you really want to create your own secret hot sauce, you should be able to find ground cayenne pepper in the spice section. A small "can full" soaked in a half bottle of Vodka for a few days, with occasional stirring/shaking, should result in a fluid sufficient to add some "bite" to almost anything without being so strong that "overdosing" is too much of a hazard.

There are other pepper varieties that are "hotter" than cayenne, but it's sort of the "standard for humans" as hot enough, but seldom fatal. Whether you can find a more potent chili pepper would depend on your local market, but as suggested the Mex section of the food/spice market is probably most likely to offer something dangerous enough.

The other half of the vodka can be used to dilute as required, and/or some mild tomato sauce or other "thickener" can be used to cut it back.

While tasting/testing to develop the degree of heat you want, remember that milk - or better a spoonfull of ice cream - is a frequently suggested treatment for restoring the taste buds for the next strength increment.

An alternative would be a jar of prepared jalapeños, pureed to a mush and mixed with whatever diluents seem appropriate. In my area, they're available in Mild, Regular, and Hot, but brand differences mean you'd want to do some testing before deciding you have the right hot for your purposes. Most prepared jalapeños do have some vinegar, so you'd have to decide whether well-drained mush suits your use.

Be bold - but don't go to dangerous.

John