In a large skillet, cook bacon over medium-high, stirring occasionally, until fat is rendered and bacon is lightly browned, about 20 minutes. With a slotted spoon, transfer bacon to paper towels to drain. Pour off all but 1 tablespoon fat from skillet (reserve for another use); add onions and garlic, and cook until onions are translucent, about 6 minutes. Add vinegar, brown sugar, maple syrup, and coffee and bring to a boil, stirring and scraping up browned bits from skillet with a wooden spoon, about 2 minutes. Add bacon and stir to combine.
Transfer mixture to a 6-quart slow cooker and cook on high, uncovered, until liquid is syrupy, 3 1/2 to 4 hours. Transfer to a food processor; pulse until coarsely chopped. Let cool, then refrigerate in airtight containers, up to 4 weeks.
Spread this savory bacon jam on bread for a holiday appetizer and send your guests home with a jar.