Prep the pork
Trim thick exterior fat from the pork shoulder, leaving some natural marbling. Pat the meat dry with paper towels so the rub sticks well.
Make the spice rub
In a small bowl mix brown sugar, smoked paprika, chili powder, cumin, mustard powder, onion powder, garlic powder, salt, and pepper until fully combined.
Season generously
Rub the spice mixture over the entire pork shoulder, pressing it into every surface.
Layer the crockpot
Scatter sliced onion across the bottom of the slow cooker. Add minced garlic. Pour in chicken broth, apple cider vinegar, and Worcestershire sauce.
Add the pork
Place the seasoned pork shoulder on top of the onions. Cover with the lid.
Cook low and slow
Cook on Low for 8 to 10 hours or on High for 5 to 6 hours. The pork is done when it shreds easily with two forks.
Shred the meat
Transfer the cooked pork to a large bowl. Skim excess fat from the cooking liquid. Shred the pork with two forks, removing large pieces of fat and any bones.
Sauce it up
Stir in BBQ sauce and one or two ladles of the cooking juices until the pork is moist and well coated. Adjust with more sauce, vinegar, or salt to taste.
Keep warm for serving
Return the sauced pork to the slow cooker and keep on warm if serving buffet style.
Serve
Spoon onto toasted buns with pickles and coleslaw. You can also serve it in tacos, baked potatoes, or grain bowls.