Everyone is at Whistlin' Willys for Stan's 10th birthday party. Cartman is anxious for Stan to open his presents cause every time Stan gets one, Cartman's mother is going to give him one. Stan's mother won't let him keep the "tween wave" Gersploosh CD that Kyle gave him; not because he's too young, but because the music sounds like crap. Randy tries to lobby on Stan's behalf. Sharon gives Randy the CD to listen to, and listen he does. The music does sound like crap; but he won't admit it to her, because he still wants to be young and hip. CNN reports on "Tween Wave", where a bunch of old people rant about the crappy sounding music and a bunch of young people rant about the old people. The boy's parents (sans Randy who is with the boys) tell them they are no longer allowed to listen to "tween wave." Gerald puts on a Police CD for the boys to listen to, but all they hear is crap. Later that night in bed, Stan pulls out his iPod to listen to some "tween wave" but all of sudden the music is starting to sound like crap to him. The next morning at the bus stop the boys are grooving out to the "tween wave". When Stan arrives he pulls Kyle aside and admits to him he doesn't like the new Gersploosh album. He admits to it sounding like crap. He goes to see a doctor, the doctor tells him it is perfectly normal. Stan is getting older, and his tastes are changing. Whether it is "tween wave" or Bob Dylan is sounding like crap to him. The doctor tells Stan that he suffers from "being a cynical asshole." In fact the doctor tells him he'll soon find everything is shitty; exemplified when Stan sees the doctor talking, but shit is coming out of his mouth.
Randy is still trying to be hip, but his wife knows better. When she tells Randy that anyone can play that crap, he gets an idea and takes to the stage as "Steamy Ray Vaughn." He starts playing his guitar and "shits his britches" into the microphone. He tells the few people at the bowling alley they don't understand his music 'cos they're old. A guy who was at the bowling alley talks with a friend about the "tweens" and about this Steamy Ray Vaughn loading up his britches. Stan returns from the doctor, and tells Kenny, Kyle and Cartman that he was diagnosed with cynicism. In fact, Stan has become very cynical in his old age; he doesn't want anything to do with the game the boys are playing. The boys all go for ice cream, but Stan says his looks like shit; then Kyle suggest they go to the mall. Randy has a crowd building, including the guy from the other night and his friend. Randy has a special guest performing with him tonight; "Steamy Nicks". The two fellows are concerned about Randy's britches. Meanwhile, Stan is alone at a diner, all his friends are sick; that is until he seems them all walk by. He confronts them, Cartman and Kenny take off, leaving Kyle behind to talk with cynical Stan. Kyle tells the Stan the truth about why they lied to him. Stan convinces Kyle to let him go to the movie with them and he promises not to make any comments. The boys all go to see "X-Men First " Inside the theatre, the boys are the only kids there, everyone else is much older; leaving Stan to comment "Oh shit."
During the coming attractions, Stan sees the previews for what they are, all shit and he comments on it. Well Kyle and the other boys have had enough, and they leave. Stan follows them out, and Kyle is again left behind to talk with Stan. Suddenly Stan sees Kyle transform into a spewing pile of shit. At the Marsh home, Randy and Sharon are having a fight; the bowling alley guys sneak into their house to save Randy's britches. Randy and Sharon's fight comes to an end, when they decide that each other has become to shitty to one another. It looks like the Marshes are splitting up. A montage begins to sound of Stevie Nicks singing with Fleetwood Mac the song "Landslide". At Stark's Pond Stan is reflecting on things, at the Marsh home, boxes are being packed. Randy tells Stan what's going on. The house is put up for sale and Randy hits the road in a moving van. Stan, his mom (and presumably Shelly) move into their new home. The two bowling alley guys are arrested. Kyle and Cartman are playing video games together and finally we find Stan laying in bed staring at the ceiling.