Put a small saucer in the freezer. Put on a pair of latex gloves to handle the peppers. Think twice before skipping this step.

Stem jalapeños (remove seeds for milder finished dish), and slice; repeat with sweet red peppers. Set aside.

Place sugar and vinegar in a heavy saucepan. Place over medium-high heat; stir constantly until sugar dissolves. Bring to a rolling boil, reduce the heat to medium, and cook, stirring occasionally, until reduced by half, 5 to 10 minutes. Reduce heat and simmer until temperature reaches 225ºF and the syrup thickens when dripped onto the chilled saucer. Add the tequila, peppers, and onion, bring to a simmer, and cook, stirring occasionally, until peppers begin to soften, about 5 minutes. Remove from the heat and allow to cool slightly; using a slotted spoon, transfer to clean jars. Ladle enough of the syrup over the peppers to cover completely; cover tightly and refrigerate at least 48 hours before serving. Reserve any leftover syrup for glazing wings or pork chops; use it to sweeten vinaigrettes for salads, etc.