Cut the pork shoulder into 2-inch cubes. Add the pork to the bowl of the slow cooker.
Add the chipotles in adobo, pineapple, red onion, chili powder, lime juice, white vinegar, salt, cumin and black pepper to a blender or food processor. Puree until the mixture is completely smooth, about 30-60 seconds. Stir in the beer until it is evenly combined. Then pour the mixture on top of the pork, and toss until the pork is evenly coated.
Cook on low for 8-10 hours, or on high for 4-5 hours, until the pork is completely tender and shreds easily with a fork. Use two forks to shred the pork, then toss it in the remaining juices.
Serve warm on tortillas, garnished with optional toppings.