A jean vest. Also known as a denim vest. Very hideous. In the 1970's and 80's often people would sport Jests with rhinestone jewelry sewn in on the back. Widely shunned since the late 90's, Jests are currently only worn by bikers, homosexuals, and serial killers.
"Honey, I don't want you dating that boy. He wore a jest, so he's either a fag or a serial killer"