Cook bacon in a skillet until crisp, then drain on paper towels.

In the same skillet, sauté onions until softened, then add garlic and cook until fragrant.

Combine cooked bacon, onions, garlic, apple cider vinegar, dark brown sugar, maple syrup, brewed coffee, and red pepper flakes in a slow cooker.

Cook on low for 4 hours, stirring occasionally, until thickened.

Allow to cool and store in jars.