Dancing Pants

Then I was deep within the woods
When, suddenly, I spied them.
I saw a pair of pale green pants
With nobody inside them!

—Dr. Seuss

Clothes can do a lot of things when worn by people. It can keep them warm, it can make them look cool, it can give them super-powers or turn them violently evil.

There are some weird articles of clothing that don't have to be worn by anyone to do things: somehow, they can move around with nobody inside 'em. For some reason, the disembodied clothing is usually a pair of pants.

Compare Animated Armor.

Not to be confused with Magic Pants, Traveling Pants, Plot Pants, Leather Pants or Brown Pants.

Examples of Dancing Pants include:

Comic Books

One Calvin and Hobbes strip had Calvin's clothes jump him and put themselves on him in odd combinations. His mother then scolds him for dressing improperly, to which he responds, "You think I wanted to dress this way?"
Iron Man has had at least one suit of his Powered Armor become sentient (and start acting disturbingly like an abusive boyfriend).
The first issue of the Roger Rabbit comic books featured as a villain a sentient set of "fancy pants," which talked like a gangster most of the time but got eloquent when wishing it would meet a pair of "female pants" to end its loneliness. This was pretty much par for the course.
In Tales of the Unexpected Azzarello and Chiang's Doctor Thirteen backup featured a pile of superhero costumes attacking the obscure band of characters as a statement about how the company ignores the stranger heroes in favor of big-name heroes that are ultimately nothing but sales icons.

Doctor Thirteen: No father wants to see his daughter become a fashion victim.

- YEEEEEEAAAAAAHHHHHHH!
One Bronze Age Superman story had the Man Of Steel dealing with his entire Clark Kent disguise having a life of its own. He finds out that he passed through a cloud in space consisting of microscopic sentient beings that got attached to his clothing and he ends up taking them home.

Film

The classic visual version comes from the Universal version of The Invisible Man. Of course, the pants aren't really dancing on their own (and singing "here were go gathering nuts in May"), but don't tell that to the villagers.
One of Mike Jittlov's demo reels in The Wizard of Speed and Time.
There's a full magic suit in The Movie of My Favorite Martian.
Plenty of clothes, including pants, danced in the Walt Disney movie Bedknobs and Broomsticks, thanks to the Substitutiary Locomotion spell.
The movie Legend had a dancing (and possibly evil) dress. When the princess danced with it she ended up wearing it.

Literature

Named for a Shel Silverstein poem in Where The Sidewalk Ends.
The Pale Green Pants With Nobody Inside Them from the Dr. Seuss story What Was I Afraid Of? Scary-looking, but quite harmless.
In Reaper Man, the surplus life force causes clothing and other inanimate objects to get up and walk (or, more accurately, run) around on their own. In particular the wizards notice a full suit running off, followed by another pair of trousers, chased by a man shouting "I paid seven dollars for you!" Ridcully is astonished by this; he didn't know there was a tailor in the city who'd include a spare pair of pants with a seven dollar suit.

"If it comes round again, trip it up. I want to see the label."

There is a Japanese children's picture book about a little boy who dawdles getting dressed, so his pants run off without him and he has to chase them. Basically, a silly story about not being late.
The villains of Larklight's second book are aliens from near the end of time called Moobs, which disguise themselves as clothes (mostly hats) and can take control of or telepathically communicate with people who wear them.

Live-Action TV

iCarly has a bra that tells unscary scary stories.
- A broken washing machine would be pretty terrifying to a bra.
Willow does this with magic to one of Tara's shirts on Buffy the Vampire Slayer, to try and cope with being lonely.

Music Video

The video to Herbie Hancock's "Rock It". (Warning: May be creepy for some}.

Tabletop Games

There's a D&D monster named a ragamuffyn, which is usually a cloud of sentient magical clothing. It also comes in varieties that are made of rags or weapons.

Video Games

One level in Monster Party has pants that are (of course) trying to kill you.
Ghostbusters the Video Game includes a collectible object in the form of a pair of patched jeans that walk about with faint disco music playing in the background. After the player collects them, they can be seen (and heard) wandering about the firehouse.
The titular hero of Plok is a being made up of clothes who can fire out his arms and legs at will.
One of the most dreaded monsters in Dragon Age: Awakening are the horrifiying schleets, which look like ordinary pairs of pants. When you get close enough, they jump up and tear out your eyes in order to lay their eggs in your eye sockets. At least, that's what Oghren's heard.

""What kind of moron do you think I am? Schleets don't lay eggs!"

Web Comics

In Adventurers!!, Ardam randomly encounters one pair of evil pants. The sheer stupidity of an article of clothing apparently trying to kill him sends him into shock.
In one Sluggy Freelance storyline, Gwynn enchants a pile of laundry and clutter to become a Clutter Monster which would force Torg to clean up their apartment. It died when they put away some of the clothes that it was using for vital organs.

Western Animation

This happened in the pilot episode of The Adventures of Jimmy Neutron, "When Pants Attack".
One of the Arthur episodes had a humiliating incident in which Arthur's pants fell down at school inspire a dream where his pants were trying to eat him. Go figure.
Darkwing Duck had an alien planet of mind-controlling hats (a literal Planet of Hats, if you will).
One Looney Tunes short involves Porky Pig getting sentenced by the Leprechauns to "The Wearin' o' the Green Shoes"!
The Techno-Trousers from the Wallace and Gromit short "The Wrong Trousers".
In an episode of Phineas and Ferb Doofenshmirtz attempted to create a ray that would dry his clothes after his dryer broke, but instead made one that made anything hit with it dance... which includes his clothes. "Still sopping wet..."
- "Summer Belongs to You" features the Klimpaloon, an animated "old-timey bathing suit" that lives in the Himalayas." "NANG NANG NANG NANG NANG NANG NANG NANG NANG NANG NANG"
Eek! The Cat has a character named Clutter, a living pile of laundry.
Greenbeard's gloves in Jackie Chan Adventures, which can move under their own power and force whoever's wearing them to steal things.
An episode of Johnny Test had Johnny's genius sisters create a pair of pants that increased his intellect called Super Smarty Pants. It developed sentience as well as Yandere traits towards Johnny, including trying to kill a love interest (whom he repeatedly denied he did have feelings for).