Spray the slow cooker with non-stick cooking spray (or use a slow cooker liner to make clean up a breeze!).
Take your slab of ribs (make sure that they are defrosted) and cut into individual slabs (about 2-3 ribs each). Throw the ribs into the slow cooker.
Mix the pineapple juice and brown sugar together and pour over the ribs. Put the lid back on the slow cooker and cook on HIGH for 7-8 hours or LOW for 10-12 hours.
After they are done in the slow cooker, use tongs to gently pull them out (they will literally fall apart when you touch them). Turn the grill on medium heat. While the grill is warming up, mix together the bottle of BBQ sauce and the 1/4 cup of pineapple juice you saved from earlier.
Place the ribs gently on the grill and and brush with BBQ sauce. Turn the ribs twice, slathering with more sauce each time (you can’t have enough sauce!); they will take about 10-15 minutes to glaze over (as soon as that sauce starts to turn sticky, you know they are done!).