In a microwave-safe bowl or liquid measuring cup with a spout, combine the honey, red pepper flakes, and cayenne (you can also warm them together in a small saucepan on the stove). The honey will bubble, so make sure you have some room for the liquid to expand.

Microwave on high until the honey starts to bubble, about 45 seconds to 1 minute, depending on your microwave. Stir, then set aside to cool and infuse for 15 minutes, or 30 minutes for a spicier honey. Taste and assess the heat level; if you'd like it even spicier, add more red pepper flakes and let sit for 15 additional minutes, then taste and assess again.

Once the honey is at your desired heat level, stir in the apple cider vinegar. Warm it again to thin the honey out (this will make it easier to pass through a sieve). Strain through a fine mesh sieve into a storage container (I use a small mason jar). Let cool completely, then cover tightly and store at room temperature or in the refrigerator for up to 3 months.