In Axis Powers Hetalia, England and America, mutual tsunderes, are both stranded on an uninhabited island together. They both end up acting as The Millstone to each other during their time stuck on the island.
England: Why did I have to be stuck with you? America: But at least it can't get any worse. Being stuck with you is pretty much the worst thing imaginable.
Ukitake's Story Mode in Bleach: The Blade of Fate is based off this trope. His Incurable Cough of Death causes him to cough up blood... onto Byakuya Kuchiki's robes. He manages to escape, but then coughs up more blood... onto Ishida Uryu's robes. Escaping again, he then coughs up more blood... onto Mayuri Kurotsuchi's robes. Thankfully for us, the players, the storyline ends after that.
This trope is exploited by Ranma in an old fanfic from the 1990s, Smartarse 1/2 when he beats up Kuno for the first time and writes something on Kuno's forehead, the twist is that it was the phrase "At least it can't possibly get any worse.". When Kuno reads the phrase out loud, suddenly a real battleaxe of a nurse walks in while putting on a rubber glove and orders Kuno to bend over... much screaming occurs.
Films — Live-Action
Played in Harold And Kumar Go To White Castle: Immediately after complaining that he doesn't know how much more he can take, Harold gets attacked by a raccoon that snuck into the car.
Subverted in Christmas Vacation: "Worse? How could it get any worse? Take a look around you, Ellen, we're at the threshold of Hell!" Things do actually start to get better at that point, and ultimately Clark Griswold gets his one true happy ending of the whole series.
Look Who's Talking, with the mother complaining about the chores of motherhood, and then being visited by her mother.
Played with in Monty Python's Life of Brian, when a Jewish Official is about to have a man named Matthias stoned to death for saying "Jehovah" (saying the name of God was a blasphemy).
Matthias: Look, I don't think it should be a sin, just for saying "Jehovah". [Everyone gasps] Jewish Official: You're only making it worse for yourself! Matthias: Making it worse? How can it be worse? [Begins dancing] Jehovah! Jehovah! Jehovah!
A classic version in Star Wars IV: A New Hope where the heroes are in the trash compactor and Han complains about the situation. Leia retorts that it could be worse, only for all to hear a sound ominous enough for Han to go, "It's worse." Shortly afterward, Luke gets attacked by a dionaga. And then the walls start closing in.
Very Bad Things is practically an endless string of consecutive rock bottoms.
Film/Bridesmaids has a few moments like this.
Annie: Remember when you though I hit bottom? That wasn't bottom!
The Wizard of Speed and Time has some fun with this trope in a sequence where the main character is attempting to film a stop-motion animation sequence in his garage. With wind. And bats. And a monsoon. And an earthquake. Eventually the main character says "or it could be quiet..." at which point the earthquake, monsoon and wind all stop (presumably the bats leave, too, but they're inside by this point).
D.E.B.S. When Janet, Max, and Dominique are trapped in the bank vault, Janet says "This could not get any worse!". Cue spikes extending from the ceiling and the ceiling starting to lower toward our heroines.
Jane: Things couldn't possibly get any worse... Thunder clashes, rain begins. Jane: Obviously it can.
Repeatedly used in a particularly dark fashion in Schindler's List. As the persecuted Jews are forced to live under increasingly more inhuman and nightmarish conditions by the Nazis, they try to cheer themselves up because their situation couldn't get even worse than it already is. That is before they discover what the Holocaust entailed.
Films — Western Animation
In The Road to El Dorado our heroes Tulio and Miguel end up stranded in a rowboat with a horse, hundreds of miles from land, with limited supplies.
Miguel: At least things can't get any- (A thunderclap sounds and it is suddenly pouring rain) Tulio: Excuse me, were you about to say WORSE?
Shakespeare's King Lear plays this straight. Edgar is betrayed and slandered by his half-brother and disowned by his father. He's now a starving beggar. He consoles himself with the thought that now the worst has happened to him, and he doesn't have anything more to be afraid of. Immediately his blinded father is led onstage.
"O gods! Who is't can say 'I am at the worst'? I am worse than e'er I was. ...And worse I may be yet: the worst is not so long as we can say 'This is the worst.'"
Dawn: Things can't get any worse, right? (an arrow embeds itself in the wall next to her) Buffy: You know this is your fault for saying that, right?
In Greek, after living with super-annoying by-the-book consultant Lizzie for a month, Casey comments that "We've hit rock bottom, and there's nowhere to go but up." On cue, Lizzie announces she's arranged a mixer...with the geekiest frat on campus.
Early in LOST's first season, Jack tells Hurley, "Things could be worse," to which Hurley replies, "How?" This is the episode in which we first learn of the Others.
In Sanford and Son the pair have a disastrous camping trip and Lamont notes that it could be worse. When his father asks how, Lamont notes "It could snow." Sure enough, it instantly starts snowing right there and then.
While it's not actually said in Supernatural, the boys (Sam, specifically) get a hold of a cursed rabbit's foot. As long as it's in Sam's possession, it'll give them good luck. If Sam loses it, he'll be dead in a week. Within a minute of losing the foot, Sam spills hot coffee in his lap, knocks over a waiter, and slips on the pavement. Prompting Dean to ask "I wonder how bad (this luck is going to get)." Elsewhere, a couple of hunters find Sam's picture on that restaurant's website, starting their hunt for poor Sam. Even though "It can't get worse," the thought is definitely there.
Played straight in The 10th Kingdom: Virginia despondently sits down on a set of steps in Kissing Town after she finds out Wolf spent all the money he'd won at gambling on dinner instead of buying the Traveling mirror, and subsequently walks out on him, thinking he's a selfish bastard who doesn't really love her. She decides, and says aloud that at least things can't get any worse. At exactly that moment, her father Tony, climbing around on the roof, loses his hold on the Traveling mirror, and it falls off to smash into a thousand pieces at Virginia's feet. The fact that this gives Tony seven years' bad luckreally shows she shouldn't have said that.
That's So Raven: Raven got stuck in a limo's moon roof when going to prom. Then it started raining on her. "Well at least it can't get any worse"...cue the gale force winds.
Vala: We're already trapped in here, how much worse could it get?! (the ceiling begins to drop) Daniel: How about that much? Vala: I knew it was a mistake the moment I said it. The moment.
Occurs on The Wire. Most prominently at the end of season 4 when Bubbles accidentally kills Sherrod, leading him to finally enter rehab and get sober. Also at the end of season 5, McNulty seems to realize just how much he's screwed up and how much it is costing those around him. It's strongly suggested that he'll finally clean up his act.
The usually Genre Savvy Crichton has one of these in the Farscape episode "Natural Election". The crew has found a way to kill the space plant that is trying to digest Moya; Aeryn and John are tasked with taking care of it.
Aeryn: You know we don't have a contingency.
John: Eh this'll work. Unless that plant can mutate in 5 minutes - what could go wrong? Damn - I did not just say that...
To be fair, the plant didn't actually mutate, but it did break an important part of the ship and destroy the chemical they were supposed to be using to get rid of it. Oops.
In the Doctor Who episode "Cold War", the Doctor says "How could it be any worse?" regarding a Monster of the Week being loose on a submarine armed with nuclear weapons. Then the submarine, currently perched on a ledge because it can't ascend, starts to slide off (risking a literalRock Bottom).
Just when you think you're as low as you can get, someone hands you a shovel.
Inverted with the Wynonna Judd song "Rock Bottom", in which she asserts that "when you get down to nothing, you've got nothing to lose" and "there are two ways to go, straight up or sideways".
The Warhammer 40,000 book Apocalypse Reloaded relates an instance of this, with appropriately 40K results:
"Just as Sergeant Pravnaski swore that things couldn't get any worse, the wailing skies split apart and the four Daemon-engines descended on us. Commissar Bone executed the next man to make a flippant remark." - Guardsman Chjeski
The obscure musical Fade Out Fade In has the song "You Mustn't Feel Discouraged," which sounds congenially cheerful, especially when it accompanies a playful tap-dance routine, but here's how the lyrics go:
"When you think you've hit the bottom, And you're feeling mighty low, You mustn't feel discouraged— There's always one step further down you can go."
Phoenix Wright: Ace Attorney gives us the backstory of one Joe Darke, an executed multiple murderer whose interrogation is at the heart of the first game's fifth case. Apparently, he hit someone with his car. Panicking, he tried to hide the body, only to be encountered by a jogger. He killed the jogger to conceal his vehicular homicide, only to be encountered by a second witness. He killed that one, too, only to be encountered by a third witness while hiding the first three bodies! After all this, after being arrested for the four murders, he gets framed for a fifth murder!
In Bioshock, one of Peach Wilkins' audio diaries mentions Fontaine's offer to his fishermen to go into the contraband business. His exact words: "Hey, it's not like things could get much worse!" As you are already aware from the last diary of his that you picked up, they did. And as you are already aware from... the game itself ...they got even worse still.
In one of the Girl Genius 'radio plays', The Sleepy Clank, Agatha finds that they have just led the murderous clank (robot) to the just arrived gathering of the town.
Agatha: This can't get any worse... Mr. Mayor, let me explain. Mayor: There's no need! Obviously you interlopers have discovered our true nature! Lizardmen Remove Your Disquises and Slay the Mammals! Agatha <long delay> ...um... yeah... Weirder maybe.
Directly quoted and lampshaded in Ansem Retort. After hearing that Aerith and Namine are being attacked by a werepire and Axel isn't helping, Zexion says "well, at least it can't get any worse". Immediately more werepires show up and Namine yells "Oh, you dickhead!".
Ah, I guess things could be worse... Aw, what a cute bunny!
You are in my spot, toots. I'm going to have to hurt you on principle.
In Dragon Ball Abridged, Vegeta got his ass kicked by the heroes, he failed to get the Dragon Balls, and lost his tail, but said that it couldn't get any worse than that. Then he discovers that Nappa's ghost is haunting him.
Archer: Well, that's just great! She gets dinner and Dixieland and laid and I get mosquitoes and no beer and...not laid. How could this get any w - (an injured, pissed off alligator emerges from the water, growling) LET ME FINISH! ...worse. (to the gator) Okay, now, see? You ruined it. You ruined the moment.
Subverted in the forty-first episode of Avatar: The Last Airbender: The group is on the losing side of a fierce naval battle. When Sokka exclaims things couldn't get much worse, a giant sea serpent promptly pops out right behind him.
Sokka: The universe just lovesproving me wrong, doesn't it? Toph: You make it too easy. (The serpent is then hit by enemy fire and begins to attack them instead.) Sokka: Thank you, the universe!
Radio: Things could be worse, you know. Lampy: How? Radio: How what? Lampy: How could they be worse? Radio: They couldn't; I lied.
The Clone High election episode had a subversion and Lampshade Hanging. The Gandhi clone says, "At least things can't get any worse." Abe replies, "How many times have I told you not to say that? Now something worse is going to happen. I've seen it on Happy Days. 3, 2, 1..." Cleopatra (who Abe has a crush on) comes in to say that she wants to spend time alone with JFK. Gandhi then says "Things can't get any better." Abe says "It doesn't work that way," and leaves. A butterfly flies by Gandhi and gives him a dollar.
Lampshadedand subverted in Garfield and Friends, "The Incredibly Stupid Swamp Monster": Orson, Booker, and Sheldon run into the weasel, who ties them to a tree and leaves them for the barnyard to nab the chickens. Orson delivers the "Things can't possibly..." version, but Sheldon tells him not to say that, because when people say things like that in cartoon shows, things always get worse. Orson compounds the error by delivering the "How could...?" variation, and Sheldon points in the direction of some rumbling. Cue the titular Incredibly Stupid Swamp Monster (really a robot that keeps spouting random incorrect phrases and which has been covered in swamp stuff from submerging itself in it). This turns out to be a good thing, however, as the monster undoes the rope (to play jump rope) and stops the weasel (in a scene reminiscent of Bugs Bunny's Abominable Snowman).
Hey Arnold!, "The Baseball", Arnold and Gerald complain about bad seating at a baseball game, and then a section of roof suddenly falls onto the two.
Lampshaded, in The Simpsons: after a run of bad luck, Homer laments to Lenny and Carl that "Things can't get any worse". All three look around expectantly, then when nothing happens Homer says with more emphasis, "Yep, things definitely can't get any worse". Immediately after that, Smithers comes on the PA and orders Homer to report for "much worse duty".
Lampshaded and subverted in a later episode, where The Simpsons lose their house. Tossed out unto the street, Homer says, "well, it could be worse. At least it's not raining." Just then....nothing happens. "See?" says Homer, "told you it could be worse."
An episode of SpongeBob SquarePants (called, oddly enough, "Rock Bottom") had a plot based on this. After taking the wrong bus, Spongebob gets stranded in a town called Rock Bottom in a deep sea trench, and has a few moments like this as he struggles to get home.
In the episode "Pizza Delivery", Squidward and SpongeBob run out of gas miles from home. Squidward actually says "How could it get any worse" and kicks the car. The car then starts up again and drives off, leaving them stranded.
In an episode of The The Super Mario Bros. Super Show, Mario and friends are thrown into a dungeon. Mario tells Luigi that things could be worse. Luigi asks him how, and Mario tells him that the ceiling could flatten them like a pizza. Right on cue, the ceiling starts descending on them. Mario, undaunted, says that water could flood the room until they drown like rats. You know what happens next. Mario, still keeping his cool, says he could think of other things that could be worse, but Luigi promptly shuts him up.
In Teen Titans, Robin and the team are Trapped in TV Land, has continually failed to catch the criminal (who's suddenly virtually omnipotent), is soaked in swamp water, and convinced things can't get worse. Thank you, now TV literally rots the viewers' brains!
In the Family Guy episode "Brian Writes a Bestseller", Stewie is stuck without a ride and without cab fare. He says, "well, at least it's not raining." Promptly subverted when a man jumps into the shot, stabs him, and leaves without even attempting to rob him.
My Little Pony: Friendship Is Magic provides the page quote, from the scene in "Owl's Well That Ends Well" after Spike ran away from home. It gets a little better when Spike finds a warm cave full of gems, but it gets worse AGAIN when said cave turns out to be owned by a grown dragon; one who doesn't exactly go easy on trespassers.
"Best Night Ever" provides another example, from when Twilight Sparkle and Celestia walked into the big room in the grand galloping gala, finding a huge mess with the debris from several shattered pillars scattered all over the floor. Twilight said "at least it can't get any worse"; cue Fluttershy barging in, and screaming "YOU'RE GOING TO LOVE ME" at the animals that were running away from her.