Now hot peppers of many kinds dominate American cuisine and I've grown a fair number myself; ancho, Anaheim, jalapeno. But in recent years I've discovered serrano peppers. They can be used sparingly in cooking or salsas (I usually choose jalapenos instead for those purposes) but they make excellent hot pepper vinegar.
In the past I've picked them all green but this year they got away from me and began to ripen. I suspect this will make the vinegar even spicier. We're still using last year's batch - this is one of those things that gets better with sitting.
I found that the excellent Joy of Pickling by Linda Ziedrich had a recipe for something she calls Picque. Picque, or pique, is a Caribbean vinegar-based sauce that apparently is often made with pineapple rind and various herbs. This recipe is simpler and is great with kale, cooked Southern-style. It is also good as a brightener in cooking or salads where you might add a squeeze of lemon juice or other splash of acidity.
12 whole black peppercorns
1/8 t pickling salt