Johnny Cash’s famous song “A Boy Named Sue” ends with the singer vowing to name his own son George. But Charleston plaintiffs lawyer George Sink Sr. seems to regret doing just that—and now his son, George Sink Jr., is firing back.

A trademark dispute between the two lawyers in South Carolina federal court has become even more acrimonious in the last few days, with Sink Jr. claiming his father is responsible for any market confusion he now blames on his son.