Combine the vinegar, sugar, Worcestershire sauce, salt, and cayenne pepper in a medium saucepan. Heat to boiling over high heat. Reduce heat to low and simmer 5 minutes.
Meanwhile, cut pork into 1-inch-thick slices, then shred it by hand. Stir the pork into the sauce, cover, and heat through, stirring occasionally.
In a large, dry skillet over medium-high heat, toast the tortillas one at a time until crisp and slightly charred around the edges, about 1 to 2 minutes per side.
To serve, spoon some pork into the center of a tortilla. Top with cilantro, avocado, tomato, and onion. Roll.