Spycrab
This article is about the Spy's taunt, not to be confused with the cosmetic item.

Spycrab
One of the most well-known fads within Team Fortress 2 is the Spycrab. The Spycrab is an animation oversight caused by the Spy looking straight up while holding the Disguise Kit, crouching, then walking in any direction. This causes the Spy to move around in an amusing fashion that resembles a crab. Dapper Rogue, a "Catalogue for the Gentleman Scoundrel", referenced this by including a "Crab-Walking Kit" with the description "It will change your skeleton! Excruciatingly painful but worth it."
Due to its popularity, the Spycrab was included as an alternative taunt for the Disguise Kit in the Sniper vs. Spy Update, and has a 20% chance of playing.
Footage of a player doing the Spycrab can be found here.
The Spycrab has a page on Know Your Meme.
A fan-made game mode was made in honor of this fad.
A type of gambling was created in honor of this fad, known as "Spycrabbing." "Spycrabbing" has many variations, with one of the most common being two players putting items they want to gamble into a pot, facing each other and continuing to taunt with the Disguise Kit out. Under usual rules, the first person to do three Spycrab taunts loses, and the winner gets the items in the pot.
A cosmetic item called the Spycrab was made in honor of this fad.
The Carnival of Carnage map has several posters plastered around the site, one of them reading "Human Crab - Alive!", which features the Spy with his fingers "pinching" the air, a reference to this fad.

Human Crab - Alive!
Another animation error unofficially named the "Democrab" by the community derives from the Spycrab's name and its effects on the user's body. It causes a Demoman's left hand to twist awkwardly if he is holding the Conscientious Objector or other Saxxy Reskins while crouch-walking, similarly to the Spycrab.