Boogie Knights

Dancing in a suit of armour. An amusing sight, in part due to the inherent clumsiness and difficulty in moving glibly in such attire. Furthermore, a suit of armor has connotations of knightly bravery and honor—hence the humorous whiplash stemming from dancing in full plate (see also The Comically Serious).

Not to be confused with Dance Battler.

Examples of Boogie Knights include:

Eastern European Animation

Semi-example: in one of the episodes of Nu Pogodi (in a museum), Wolf disguises himself as a suit of armor and soon afterwards slides across a slippery floor, doing figure skating maneouvers to the tune of a classical melody.

Film

The "Knights of the Round Table" song from Monty Python and the Holy Grail.
The end of Ella Enchanted sees the armored castle guards dance along to the Crowd Song (since they never even speak, let alone sing).
The original 1963 version of The Pink Panther included a costume party in which Inspector Clouseau attempted to remain incognito wearing a suit of armour, complete with clanging faceplate. He spends some of the evening dancing.
Iron Man 2: Tony Stark, drunk as hell, fully suited up in Iron Man armor. And its one of the most hilarious moments in the movie.
In The Three Stooges short "Squareheads of the Round Table", Larry, Moe, and Shemp noisily dance in full armor to an "ancient" radio playing "Swanee River".
This behind-the-scenes clip from the set of Predator 2 is dripping with this trope.
Not dancing per se, but the Mel Brooks movie Silent Movie has a hilarious scene where the main characters, in full plate armor, try to eat lunch at a cafeteria.

Live-Action TV

One contestant on Britain's Got Talent did a Michael Jackson dance dressed as Darth Vader.
Canadian comedy duo Johnny Wayne and Frank Shuster once had a TV special that parodied fairy tales - they star as a court jester and royal physician, breaking into an impromptu softshoe dance in the dining hall, followed by a knight in armor doing a more vigorous tapdance.

"That's not softshoe, that's heavy metal!"
"My mom told be there'd be knights like this..."

Tokumei Sentai Gobusters features the Red Buster's Humongous Mecha dancing to the ending song.
- Predated by Hyakujuu Sentai Gaoranger, where a bored Yabaiba (no, it's not For the Evulz) holds Tetomu hostage so the Gaorangers would make Gao King dance.
In MythBusters, Adam Savage sometimes dances in their fire suit.

Music

A very non-humorous example is Prokofiev's Dance of the Knights, which may count as Crowning Music of Awesome.
Adam Ant dances in a very shiny suit of armor in "Ant Rap".

Tabletop Games

Knight of the Hokey Pokey, from the Unglued joke set of Magic: The Gathering.

Theatre

In Spamalot, Robin would rather sing and dance than fight, and eventually pursues a career in musical theater. Lancelot, a Invisible to Gaydar, is also revealed as loving to dance.

Video Games

In RuneScape, if you pay some money and pull a lever at the party room (formerly in Camelot), a group of knights would dance and sing on a table. Probably inspired by the Monty Python and the Holy Grail scene. Also, there are multiple dance emotes, which players can do in full armor.
World of Warcraft. The dance command is never affected by whatever your character is equipped with.
Both Mass Effect and its sequel allow the protagonist some dance steps in full combat gear.
In The Sims Medieval, when a musician plays a lute, most people in the room start to dance; this includes any knights in full armor, and occasionally even golems.

Web Comics

The "Dancing Knights" spell in Order of the Stick, a pun on the "Dancing Lights" spell found in Dungeons & Dragons.

Real Life

Longsword instructor Guy Windsor once explained the versatility of armour by stating that an armoured knight can "run, jump, ride and even dance techno. I have seen this with my own eyes."