|Source: Stop, Cassie! fanfic|
A "chocolate wagon" is a euphemism for poop. The term itself is sourced from a Dragon Tales fanfiction titled "Stop, Cassie!" where the author refers to fecal matter as a "chocolate wagon" dozens of times throughout the story. This story, as well as a follow-up from the same author named "Dulcy's Bad Case", were featured on Fanfiction Factory.
Due to the bizarre nature of the euphemism it became an immediate hit with the channel and in a matter of days the chocolate wagon was added as a FrankerFaceZ Twitch emote. The emote was initially chosen by ElectricSheepCity to redeem his Patreon reward tier, however its popularity eventually resulted in the emote becoming a permanent addition. The emote itself is a sprite of the wagon from the MS-DOS version of The Oregon Trail colored brown. It retains its original definition from the fanfic and is sometimes used in a negative manner to imply something is of poor quality.
To this day nobody is quite certain how or where the fanfic author came up with the term "chocolate wagon". The closest the community has come to finding a possible source is a "wagon wheel", a chocolate-covered graham cracker and marshmallow cookie. However additional stories written by the author have introduced the terms "chocolate pears", "chocolate bananas", and "chocolate ketchup". It was revealed in "Dulcy's Bad Case" that the "wagon" part is meant to be literal and that the droppings look like Radio Flyer wagons.