Place a large skillet over medium-high heat. Cook the bacon, stirring occasionally, until the fat is rendered and the bacon is lightly browned. Use a slotted spoon to transfer the bacon to paper towel-lined plate to drain.
Pour off all but 1 tablespoon of the bacon grease from the skillet. (You can reserve the rest of the grease for another use.)
Add the onions and garlic to the skillet and cook until onions are translucent, about 6 minutes
Add the vinegar, brown sugar, maple syrup, red pepper flakes, and coffee to the skillet. Bring everything to a boil, stirring and scraping up browned bits from bottom with a wooden spoon. Cook for 2 minutes, add in the bacon, and stir to combine.
Transfer mixture to a slow cooker and cook uncovered on HIGH for 3 1/2 to 4 hours, until the liquid is syrupy.
Transfer the bacon jam to a food processor and pulse until it's coarsely chopped.
Let the jam cool, and then refrigerate in an airtight container for up to 4 weeks. (or freeze for up to 6 months)