"Shirt Herpes" is the 3rd episode of Season 9 and the 113th overall of Aqua Something You Know Whatever.
Carl tells Shake the tale of thousands of years ago, when he ruled sexy cave women and fought ancient demons. After explaining the story, Carl tells Shake that he must pass down his shirt to someone after thousands of years, and that the shirt wants Shake for a new generation. Shake puts it on him, and later that night, he has a nightmare that he is riding a small purple dragon up the volcano Carl rode once to defeat the dark lord, and is confronted by two minions of Satan. Shake explains that he is the new ruler, and they explain there are eighteen more shirts that he owns. They yank Shake in the fire pit, Shake wakes up, and can't get the shirt off. Carl goes in the pool and it is revealed that Carl chose Shake because he didn't like the shirt, and tricked him into wearing it because the shirt causes odd dreams and is very tight. Shake has another dream and meets another with the shirt. Shake has another dream, and the demons then tell him that he must find someone else to wear it, or he will be raped by an octopus and Shake wakes up again. Frylock examines the shirt, and it is revealed the shirt is making its way to the brain, and that it is merged to his flesh. If they cut the shirt off, Shake will die. While being raped by the octopus, Shake tries to get out of it by breaking up with him, but allows a quickie. He says that he can't get used to it, but is glad that he's not dead.
- Shake is killed during one of his dreams.
- An unnamed man with the magical shirt is shown to be dead in the background.
- This is the the only episode in the series to be rated TV-MA-S.
- According to Dave Willis, this is the third episode they have done involving a magical shirt.
- This marks the 2nd episode since Wi-tri had Shake used the line "Damn, son!"
- Although Shake completes Carl's sentence with the "one eyed wonder worm", Carl is clearly riding a weasel-like creature. If Shake was meant to say "one eyed wonder weasel" then it was most likely a reference to Super Trivia where Carl names the team "The One Eyed Wonder Weasels and Their Two Balls".
- The song heard in the background of the Inner Planetary Insanitarium was by Progressive Metal band Queensryche.