Hot Tub High School is a low-budget movie released in 2000. A young Chloe Decker appeared naked in the film. There is apparently a sequel entitled Hot Tub Hotel that Chloe did not appear in.
History
In "Pilot", Lucifer remembers seeing Chloe in the movie.
In "Lucifer, Stay. Good Devil.", Chloe Decker talks with her daughter about the film. Surprisingly to Chloe, her daughter had already seen the film.
In "Everything's Coming Up Lucifer", Lucifer mentions the movie title to Chloe.
In a flashback in "My Little Monkey", John Decker, Chloe's father, gives tickets to the film to Petey, a Korean shop owner. He refers to Chloe as "My Little Monkey" and says he's proud of her. Petey mentions the "funny business" about 15 minutes in and John asks Petey to tell Chloe that the movie was good.
In "They're Back, Aren't They?", a suspect believes that Chloe and Lucifer coming to arrest him is a prank played by his friend, the victim of the episode. When confronted by them, the suspect states that he thought it was a prank because he was confronted with a man named Lucifer and Chloe who he recognized as "the chick from Hot Tub Hotel." Lucifer tells the suspect it was actually Hot Tub High School and that "she wasn't in the sequel."