Arsenal Attire

There are times when even the most awkward looking clothing will turn out to be a lethal weapon.

The princess in the ball gown?

She spins and a fringe of razorblades flips out.

That guy in the top hat?

It's made of magical caterpillar silk and will block a gunshot or cut your head off.

The dancer 'wearing' nothing but fans?

She flips them backward and they will decapitate you.

The guy eating soup in the truck stop?

His bandana is made of armor plates that will stop a bullet and/or break your face.

Do you ever wonder why they call them 'stiletto' heels?

Many heroes will wear armor and weapons that are invisible to casual observation because they look like part of their normal clothing. This has many advantages, not the least of which is being able to take them places where weapons are not normally allowed.

This kind of double purpose clothes are a common hallmark of a Badass. This trope is sometimes a Sub-Trope of Clothes Make the Superman and Clothing Combat, but not always. It is often a Super-Trope to Hat of Power.Weaponized Headgear and Sword Cane are Subtropes.

Real Life

 * The Asiatic practice of making 'weighted sleeves'.
 * Ninjas did this sort of thing constantly.

Comic Books

 * Gunsmith Cats: Bean Bandit's outfits.
 * Lady Killer from The Strangers in The Ultraverse was a superhero who was also a fashion designer. Every part of her costume could be used as a weapon.

Film

 * Oddjob's razor brimmed bowler hat.

Literature

 * The Lookingglass Wars series: The entire Millenary, but Hatter Madiagan's wardrobe in particular.
 * Discworld:
 * Adorabell Dearhart, AKA "Spike", AKA "Killer", has stiletto heals that can punch through two reinforced layers of cured leather and a human foot and still embed themselves into an oak floor board.
 * Sam Vimes butler Wilkins used to own a hat with Sharpened pennies sewn into the brim for fighting; when he was a street ruffian in his youth.

Tabletop RPG

 * Shadowrun. The 2nd Edition supplement The Neo-Anarchists' Guide to Real Life had a section dedicated to armor and weapons disguised as clothing. They included the Barton Arms Bracer (a gun disguised as a piece of jewelry) and the Barton Arms Gun Cane (a cane that can fire a bullet). A variety of fashion houses (Armante, Mortimer of London, Vashon Island and Zoe) have formal wear that could stop a bullet.
 * D&D : Monks; everything they wear can be used as a weapon.

Video Games
": He's covered from head to toe in weaponry. Like a rainbow apocalypse.
 * in Kid Icarus Uprising.
 * I prefer to think of it as my devastation ensemble. I only wear it for very special occasions. You know, weddings, armageddons..."

Web Comics

 * In Schlock Mercenary, the standard uniform for Tagon's Toughs is actually nanofiber armor with a deployable breathmask and allows antigrav flight as well.