Parodied in The Simpsons episode "Guess Who's Coming to Criticize Dinner", with Homer sitting in a tub, looking traumatized with wide eyes as he crazily scrubs at his skin repeating, "Still not clean, stink of failure still on me! Still not clean, Stillnotclean!" after the newspaper editor rejected his first draft of his food review.
Not exactly a shower, but in "Black Widower", Sideshow Bob splashed water from the sink all over his body after making love to Selma.
In the Drawn Together episode "Requiem for a Reality Show", after Captain Hero degrades himself sexually to Foxxy Love in exchange for food, we see him sitting in the Shower of Angst eating cookies.
Parodied in a Family Guy cutaway, where Darth Vader showers in a depressed manner after a hard day at his job as a meter maid, and just before he resolves to apply for a loan to build the Death Star. On the commentary, Seth MacFarlane refers to the trope, saying every pretentious independent film needs to have an obligatory scene where the character "showers the pain away".
Parodied again when Peter the Strawberry took one after being "violated" by a worm.
"He was my neighbor...and he violated me! Now I'll never know the inside of a fancy pie!"
Stewie sits fully clothed under the shower spray crying as he washes Rupert after learning that New Brian humped Rupert.
Brian does this when he finds out that the women he slept with the prior night was Ida, Quagmire's post-op dad.
Murderface does this in an episode of Metalocalypse after a gay doctor accidentally (or not) jerks Murderface off in his face and he goes into a state of paranoia about his own sexuality. Later mirrored in a still-shower-based Redemption in the Rain moment when Murderface finds out that it was the doctor, not him, who was gay.
In the Spongebob Square Pants episode "Squid's Day Off", Squidward goes crazy from paranoia after leaving Spongebob at the Krusty Krab by himself and tries to take a bubble bath to calm himself down. He ends up hallucinating while in the bath and seeing Spongebob everywhere.
In The Ren & Stimpy Show Ren who is exhausted from work, and Stimpy's nonsense, takes a bath in very dirty water, while wearing lipstick.
In the Regular Show Episode Muscle Woman, Muscleman, who is distraught after breaking up with his girlfriend, spends a lot of time crying in the shower.
South Park: One of the scenes opening "Ass Burgers" which show Stan with a disaffected, sad face have him standing in the shower, standing still just like this.