The "Thagomizer", Gary Larson's legendary term for the only dangerous part of a Stegosaurus. Now a scientific term!
Rest assured, this is printed on the back of the Tshirt :)
"The term "thagomizer" was coined by Gary Larson in a 1982 Far Side comic strip, in which a group of cavemen in a faux-modern lecture hall are taught by their caveman professor that the spikes were named "after the late Thag Simmons". The term was picked up initially by Ken Carpenter, a palaeontologist 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."