Staircase Tumble

Alas, even with extensive warning about the staircase...

"I WARNED YOU ABOUT STAIRS BRO!!!! I TOLD YOU DOG!"

—Hella Jeff, Sweet Bro and Hella Jeff (sic)

Stairs can be dangerous if you misstep and fall down, even worse depending on how long it is. Still, it can be funny, especially in cartoons.

This is one of the common ways a Fright Deathtrap is used to kill someone. It can be caused by a case of Mind Your Step, but there are plenty of ways to misstep and fall without the stairs containing a trap or problem.

Examples of Staircase Tumble include:

Anime and Manga

Nobita from Doraemon has fallen down the stairs many times with comedic results.
Played with horribly with Yukari in Another. She falls down the stairs which is bad enough, but what kills her is getting Impaled with Extreme Prejudice through the neck... on the metal tip of her umbrella.

Comic Books

In what could be the most evil and mean-spirited example of this trope, in Ultimate X-Men, Mr. Sinister introduces Professor Xavier to "his one enemy... stairs". (If you're not an X-Men fan, Xavier is wheelchair-bound.) The image of this quickly became meme-worthy.

Film

In the movie Surf Ninjas, during the final epic battle, an enemy Mooks gets knocked down a flight of stairs that runs up the entire mountainside. He manages to climb back up before the battle ends but gets knocked down a second time. By the time he gets back up again the battle's ended and when told "It's over. Your side lost." He shrugs and willingly throws himself down the stairs again.
I'm Gonna Git You Sucka: as a Running Gag, each time Mr. Big's two Mooks Leonard and Willie get captured by the good guys or screw up a mission they're given the option of going out the window or down the stairs. They almost always choose the stairs, after which the camera cuts to a scene of them tumbling painfully down the stairs.
Used as a recurring joke in Kung Fu Panda, in reference to actual stairs on ancient shrines, and how out of shape Po is.
A non-malicious example: in Cloudy with a Chance of Meatballs, Sam pushes Flint down the bouncy stairs in the Jell-O Castle.
Pinocchio did this on stage at the start of his number "I've Got No Strings." Not really injurious, but humiliating.
In Indiana Jones and the Last Crusade, Indy and his dad escape through Castle Brunwald only to find themselves at a dead end. Indy tries looking for a secret exit; his dad ends up finding it when he sits down and leans back in a chair, revealing a hidden staircase. Unfortunately, Indy was standing right on top of it at the time...

Indy: *falling down stairs* DAAAAAAD!
Henry Jones, Sr.: ...a solution presents itself!

In Death Becomes Her, Madeleine is pushed down a very long flight of marble stairs, ending in a battered heap at the bottom with her head twisted around backwards.
What Ever Happened to Baby Jane??
This is the way Nomi claws her way to the top in Showgirls.
Happens at the end of Hitchcock's remake of The Man Who Knew Too Much.

Literature

The Book Of Margery Kempe has the husband of the titular character fall down the stairs and getting heavily wounded by it, and potentially mentally challenged. He dies.
Used in several Agatha Christie books. Discussed by Hercule Poirot as a typical way of murdering rich, elderly relatives.
In Gone with the Wind, Scarlett miscarries her fourth pregnancy (ironically, the only one she was actually pleased by) after falling down the stairs.
In Dragondrums, Piemur takes a nasty spill while running up stone stairs, "courtesy" of some of his fellow apprentices "thinking" it would be funny to grease some of the steps (this bunch had earlier shown a taste for nasty pranks against him, such as "anointing" his belongings with bodily wastes while he was away).

Live Action TV

A Running Gag in My Wife and Kids is Claire falling down the steps.
The Twilight Zone episode Uncle Simon contains a fatal staircase push.

Music

Played for Laughs in Key of Awesome's parody of Ke$ha's "Tic-Toc" music video. The actress who played Kesha commented several times that the staircase scene was the hardest one she has ever done for the KOA.
Happens to the narrator in Dead Kennedys' "Too Drunk to Fuck" as a consequence of his drinking.

Nursery Rhymes

"Goosey Goosey Gander":

There I met an old man
Who wouldn't say his prayers,
So I took him by his left leg
And threw him down the stairs.

Video Games

In some Roguelikes attempting to use the stairs while confused or carrying to much weight can cause you to trip and fall down the stairs, causing you damage (and hence possibly killing you).
This was a common way to die in old adventure games, especially Sierra games, which mocked the player for the various ways in which you could get yourself killed by performing ordinary tasks. The King's Quest series is a particularly bad offender.
In Deardrops, Shinichi pushed his fellow violinist Johan down a flight of stairs on impulse, injuring him, due to stress.
In the otome Visual Novel, (P)lanets, the main character gains her telepathic powers after tripping down a flight of stairs at her school.
This is the entire point of Stair Dismount.

Web Animation

Used in Rejected as a Dead Baby Comedy.

Web Comics

Van Von Hunter: a technoleech shows Asimov, a humanoid robot that can climb stairs, to the evil prince. The prince, offended, climbs the stair after yelling "I can do that!" but trips near the top and tumbles down the stairs, disproving himself once again.
Sweet Bro and Hella Jeff: Come on, You already know how this one goes.

Sweet Bro: "FUCK IM FALLING DOWN ALL THESE STAIRS ..................."
Hella Jeff: "I WARNED YOU ABOUT STAIRS BRO!!!! I TOLD YOU DOG!"
Sweet Bro: "IT KEEPS HAPPENING"
Hella Jeff: "I TOLD YOU MAN"
Hella Jeff: "I TOLD YOU ABOUT STAIRS!"

Since Sweet Bro and Hella Jeff is Homestuck's comic within a comic and in-universe source of Memetic Mutation, callbacks to it occur any time a character falls down a flight of stairs. When Dave gets flung down some stairs, Hella Jeff pops up to declare his legendary warning on the subject. Tavros is warned against traversing any stairs until he gets more practice with his robot legs, and when he does fall (which happens repeatedly... keeps happening, you could say), it's accompanied by the Unsound Effect "HAPPEN". Later on, when Karkat is dragging Sollux to escape Gamzee, they fall down stairs simply from him not looking where he's going, and it's accompanied by "HAPPEN x2 COMBOB".
Used in The Adventures of Dr. McNinja; he gets scared by some cobwebs, trips, and falls down the stairs.
In Wapsi Square, both Monica and Tina have fallen victim to this.
Xkcd: "The stampede lasted two hours and reached the bottom three times."
Dave of CRFH tried to commit suicide by falling down the stairs. The end results were much more entertaining.

Western Animation

In The Simpsons episode "My Sister, My Sitter," a major plot point is that Lisa accidentally causes Bart to tumble down the stairs in his house. The rest of the episode is about her trying to find medical help for Bart while everyone gets the wrong impression that she had beaten Bart.
- In an early episode, Homer fell down the stairs tripping on Bart's skateboard angering at his son's hallway mess. He spent the first act laying on the couch due to his back pain.
- A Running Gag in "Bart the Mother" is Homer falling down the basement stairs due to Bart's actions.
A major subplot in Family Guy episode "Brian Griffin's House of Payne" when Chris and Meg's misbehavior pushed Stewie down the stairs causing a severe head wound.
- One cutaway gag shows Bobby McFerrin falling down the stairs.
In the Dexter's Laboratory episode "SDRAWKCAB", Dexter gets manipulated into running up and down a flight of stairs, causing his father standing next to him to get dizzy and come tumbling down.
The episode "Girlfriendklok" in Metalocalypse has Nathan's girlfriend falling down several flights of stairs, placing her in a coma.
Ed, Edd 'n' Eddy: in episode "Dear Ed"

Johnny: Wow, Ed, you go down the stairs just like Plank!

According to TF Wiki, Skywarp's favorite pastime is pushing people down the stairs.
This happens in a season 1 episode of Jackie Chan Adventures.
In Drawn Together, Princess Clara thinks she's pregnant and submits to a tumble or two down the stairs of the "M. C. Escher Room" in an attempt to force a Convenient Miscarriage.

Real Life

Tragic Truth in Television example: this is how Kaneto Shiozawa died.

IT KEEPS HAPPENING