From wikipedia

Cartoonist Gary Larson invented the name “thagomizer” in 1982 as a joke in his comic strip The Far Side, and it was gradually adopted as an informal term sometimes used within scientific circles, research, and education.

Also wikipedia

The term was picked up initially by Kenneth Carpenter, then a paleontologist at the Denver Museum of Nature and Science, who used the term when describing a fossil at the Society of Vertebrate Paleontology Annual Meeting in 1993. Thagomizer has since been adopted as an informal anatomical term and is used by the Smithsonian Institution, the Dinosaur National Monument, the book The Complete Dinosaur and the BBC documentary series Planet Dinosaur. The term has also appeared in some technical papers describing stegosaurs and related dinosaurs.

How is this still “informal” when all the big guy using that? You can’t just anthagomize someone because they aren’t from the same community!