"You're Getting Old" is the seventh episode of Season Fifteen, and the 216th overall episode of South Park. It aired on June 8, 2011.
After Stan celebrates his 10th birthday, he begins to see everything differently. The other boys think he's become a major buzzkill and start to avoid hanging out with him. When Stan and Kyle have a major blow up, the very fabric of South Park begins to unravel.
At Stan's 10th birthday party, one of his presents is the latest CD from a "Tween Wave" band. Sharon forbids Stan from listening to it, and promptly takes the CD away. Later, Randy and Sharon argue over the CD. Randy decides to sit down and listen to the CD (which, to the viewer, is the sound of farting and drum beats). He claims to enjoy the CD, but the other parents of the boys forbid them from listening to "tween wave" after playing The Police's album Synchronicity as an example of what they consider to be good music. To the boys, though, it sounds just as the "tween wave" music does to Randy. That night, Stan secretly listens to the confiscated music but discovers, to his confusion, that it now sounds "like shit." He tells Kyle this the next morning.
Afraid that something is wrong with him, Stan goes to the doctor, who initially tells him that his musical tastes are naturally changing as he grows up. During these tests, however, Stan begins to view everything he sees and hears as feces, leading the doctor to diagnose him with being a "cynical asshole". So now, from ice cream to movie trailers, Stan can now only see the bad in things. Kyle, Kenny and Cartman stop hanging out with Stan, because they think he is "a major buzzkill"; soon, Kyle and Stan say their final exclamations to each other. In the middle of this, Stan views Kyle as a large piece of feces, spewing nothing but feces, and calmly walks away, thus ending their long friendship.
Meanwhile, Randy gets caught up in the "Tween Wave" craze (in order to hold on to his childhood dreams of becoming a rockstar) and after finding out that Tween Wave is playable, he starts performing the music at the local bowling alley under the name "Steamy Ray Vaughn," repeatedly farting into his pants as part of the act. During a "duet" with a woman billing herself as "Steamy Nicks," Sharon catches Randy at the bowling alley and drags him home, resulting in a huge argument. At some point in the argument, Randy reveals that why he did many weird things (like getting into fights with other dads at baseball games, playing World of Warcraft, and becoming a celebrity chef) is because he's unhappy. The two agree that they do not feel the same about each other anymore. Two old farmers hear about the act and break into the Marshes' home to steal Randy's underwear, believing that they are acting humanely on its behalf.
While Fleetwood Mac's Landslide plays, Sharon (fed up of Randy changing his occupation all the time) and Randy apparently divorce, with Randy presumably moving out of town while Stan, Sharon, and Shelly move into a new apartment. The police recover Randy's underwear from the farmers. A new friendship appears to develop between Kyle and Cartman, who share a smile while playing Xbox together. The song ends as Stan is lying alone on his new bed, certainly doomed. The credits roll in silence.