Cut the steak in half to fit the crockpot. Rub the fajita seasoning all over it and put it on the bottom of the crockpot; poured the vinegar and corn over meat.
Cook on LOW for about 8 hours or until it is tender enough to break apart with a fork. Shred the meat and mix the juices and corn all together. Serve on flour tortillas with cheese and sour cream plus optional topping to your taste.