Using a meat injector, inject as much of the Bloody Mary Mix as you can into the pork butt. Marinate in the refrigerator for several hours, ideally overnight. Coat pork butt with salt and pepper and place in a slow cooker. Add remaining Bloody Mary Mix, red onion and garlic. Cook on low for 8-10 hours. Shred when tender. Serve with SuckerPunch pickles and salsa to really "wow" the crowds!