"Unvelked" was a phrase that meant one's shoes' velcro was undone, or unvelcro'd. This term became common with auto-lacing shoes that acted as velcro. While he harassed Marty McFly, Jr. in the Cafe 80's about the robbery that they were planning, Griff Tannen told him that his shoe was unvelked, forcing Marty Jr. to look down where Griff had his finger and getting hit in the face with Griff's hand.