He did a 'The Empire Strikes Back' Mad Magazine edition in 1980. George Lucas sent him a personal written letter telling him how much he enjoyed the issue.
A little bit later, Lucasfilm's legal department also sent Dick a threatening legal letter informing him that Mad Magazine was infringing on 'The Empire Strikes Back' copyright with the issue they had released.
Dick opened his desk drawer and took out George Lucas' personal letter praising the issue, made a copy of it, and mailed it back to Lucasfilm legal.
He never heard from them again.