I would suggest it a toss up for the title of laziest bodybuilder of all time between Flex and Paul Dillet. Both incredibly gifted genetically and just as equally lacking in the dedication department. Paul had an even greater propensity for gaining muscle than did Flex and is in all likelihood the lazier of the two, when you consider that he couldn't even be bothered to put forth a posing routine that could even at best, be called lackluster.
The above being said, I'll give Flex the title of laziest due in large part to his being so close the an Olympia title, but not seizing it. Win or lose, if one gives his all, he can at least have the satisfaction in knowing that every effort was made. When Flex looks back upon his career, he must realize that he only scratched the surface of what he could have truly accomplished. Whatever discomfiture he would have had to endure in his training and diet to be his best would have been well worth the effort, if he could look upon his mantle and see at least one Sandow. Perhaps an adequate consolation in his mind is to distract himself with hideous tattoos and ugly, albeit expensive custom rims for his rides.