Some info and a short description of this South Park episode on South Park Zone:
South Park - My Future Self 'n' Me is episode 95 of the Comedy Central series South Park. It originally aired on December 4, 2002.
In this South Park episode Stan meets a man who claims to be Stan in the future after a life of abusing drugs and alcohol, Butters will face the same problem (man who claims to be Butters in the future), thing that will push the boys to do some research.
Meanwhile, Cartman starts a business, a revenge company.
In the end Cartman says that the whole experience has taught him that he should think about the future and start taking better care of himself.
South Park Spoiler Alert!
(The complete plot for this South Park Episode)
The boys, along with Craig's Gang, find some "maria" in a secluded area, left there by some older kids. They are afraid of it, but know that they must dispose of it. Stan chooses to throw the joint away saying, "It's just a stupid plant that makes you dumb, touching it won't hurt you."That night, in the middle of a thunderstorm, a man claiming to be an older version of Stan appears at the Marsh family's door. This future Stan is in very poor condition, as apparently Stan's life has been a complete failure. He spent time in juvenile hall, used large amounts of drugs and alcohol, and has descended into being common street trash; which Stan decides must have begun when he first touched the "maria" cigarette. He is convinced that the only way to safeguard his future is for his present self to avoid drugs and alcohol, do well in school, and stay motivated in life.
Stan, horrified by the prospect of his future life, even asks Butters to tutor him. While the two boys are talking, Stan discovers that Butters also has a slovenly "Future Self" living with him.
Stan finds the whole situation suspicious, and goes home with Butters in tow to search through his "future self's" wallet. In it, he finds a key card that expires in 2002 (the present year at the time of the episode's airing). He finds an address on the back of the card (3451 Colfax Avenue) and the two find the building that it leads to, "Motivation Corp." Stan and Butters sneak in and actually see a couple hiring an actor to pose as their son's future self, and overhear a conversation the salesman and clients have about how it is okay to lie to kids if it gets them to do the things they want; in this case avoiding drugs and alcohol. Stan is appalled at the way these parents have all deceived their children (namely the way his parents deceived him), and he and Butters decide to look in the phone book to find a place to run away to. However, they discover a "Parental Revenge Center" hotline with guaranteed results, so they decide to give it a try.
The address leads them to an office in a grungy alley, where they discover that the founder and proprietor of the business is Cartman. Cartman agrees to help the two, but Stan is skeptical. Sadly, Cartman's revenge plan for both boys involves going to both of their houses to smear all of the walls with feces. Butters is delighted by this offer and gladly accepts it, while Stan believes that it isn't adequate payback. Cartman then tries to convince Stan by taking it up a notch and offering to kill his parents and slice them into pieces. Stan refuses this offer as well, and decides to worm the truth out of his parents himself in order to force them to acknowledge they lied to him.
Stan repeatedly attempts to get the truth out of his parents but fails every time with increasingly blatant lies from his parents. An example of this would be when Stan fakes cutting off his hand to see if it will happen to his "future self". Randy, not wanting to blow his cover, distracts Stan momentarily and cuts off "Future Stan's" hand. Stan then reveals that he did not really cut off his hand and Randy frantically tries to reattach Future Stan's hand, saying "Look, it was fake in the future too!" Meanwhile, the Parental Revenge Agency does its job at Butters' house as Cartman and a group of Hispanic day workers smear feces all over the living room and bedroom of the Stotch Household. Upon returning home, Chris and Linda actually acknowledge that they deserve it for lying and finally tell the truth about the "future self thing" and apologize to Butters, which surprises Stan, seeing that Cartman's plan for Butters to get revenge on his parents has really worked. Randy and Sharon Marsh arrive and continue blatantly lying to Stan, insisting that more future selves must be coming back in time to the present, which finally causes Stan to snap and tell them he knows all about Motivation Corp. and was trying to get them to admit they lied to him. Randy finally apologizes to Stan and gives him the whole truth about drug abuse, saying that it probably won't kill him or fund terrorism but still may ruin his future. Stan adds he really wishes they had just told him that in the first place instead of lying to him. The Stotches and Marshes then all agree that what Motivation Corp. does is wrong, and hires Cartman to smear their walls with feces. At that point, Stan thanks Cartman, saying that he really came through. As a reward, Stan's mother gives Cartman a box of baked cookies.
Cartman says that the whole experience has taught him that he should think about his own future and start taking better care of himself. Moments later, a thin and handsome man, claiming to be Cartman's future self, shows up and tells Cartman that this was the turning point in his life. From this day forward, he turns his life around, and will become the famous CEO of a time-traveling company. Cartman is not convinced, believing it to be yet another Motivation Corp actor and immediately changes his mind, vowing to "whatever I want!" from than on. Unfortunately, it turns out the man really is Cartman's future self and immediately changes into a fat, dirty, morbidly obese mechanic. Future Cartman then exclaims, "Oh, Goddamn it!"