Comedian Ari Shaffir performs at the 2015 Bonnaroo Music and Arts Festival in June in Manchester, Tenn. Shaffir has said fellow comedian Carlos Mencia stole his joke about who would build a fence on the U.S.-Mexican border. Copyright on jokes is difficult to prove, and it turned out two other comedians had made similar jokes as well. John Davisson/Invision/AP hide caption

itoggle caption John Davisson/Invision/AP