The absurdist, non-sequitur nature of the filename is characteristic of the humor found on anonymous imageboards like 4chan. Since its launch in 2003, 4chan has been a breeding ground for unique memes, copypasta, and viral content, and it wouldn't be surprising if a user coined this specific phrase as a joke in a motorcycle or "random" board.
: The ".11" suggests this is only one part of a larger file, meaning even a "clean" download would likely be unusable without the other 10 parts. A-Rider-Needs-No-Pants.avi.11.pdf
Adobe’s PDF specification (ISO 32000) allows embedding of multimedia files using the RichMedia annotation. An .avi could be embedded as a 3D or video object. However, the .11 suffix remains problematic. The absurdist, non-sequitur nature of the filename is