A person who does very stupid things, a dimwit.
This word is a contraction of "Cupid Stunt", who was a character on the
Kenny Everett Show in the 1980s. This in turn is a spoonerism of "Stupid
Cunt". The expression is used by
people who watched TV in the 1980s, usually to describe people who were born after show's popularity waned and are therefore unfamiliar with the expression.