A Personal Story...
..."The "Hairball" name came from the fact that we were the 13th class of astronauts, so one of the patch designs featured a black cat. That design made it all the way to the last vote, and by that time it had given us our nickname even though it didn't become our class patch"...
Astronaut - Janice E. Voss
..."Being group 13, the "unlucky" theme came up early in patch design discussions, which led to a proposal with a black cat on it. Someone mentioned that it reminded them of hairballs and we began to call ourselves that. Since then, every astronaut class has consistently had some kind of disparaging nickname, along with the 84 class before (the maggots)"...
Astronaut - Rick Searfoss, June 2001
Spot the Patch !!!
Astronaut Don Thomas with the hairballs patch on his flight suit.
Hairballs in Space...
STS-65 crewmembers who were also members of the 1990 Astronaut Class 13 (Group 13) pose in front of the sleep station on the middeck of Columbia, Orbiter Vehicle (OV) 102. During off-duty time, the four crewmembers from the 1990 class display the Group 13 insignia the "hairballs".