Lucille Ball was an American actress and comedian whose television show, I Love Lucy which ran from 1950 to 1957 (yes, I'm old enough to remember it) is still being shown in reruns around the world. The TV show featured a similar plot in every episode: Lucy would think up some crazy scheme (like to perform in her husband's band or earn extra money) and the scheme would go wrong. Lucy would wind up in an awkward situation which she would make worse by compounding her mistakes. Eventually the mess would get so bad that she would have to confess everything to her husband and beg forgiveness.
A Lucy moment is when your plans backfire on you because of your own impulsive behavior and create public humiliation, which, of course, is funny to everyone but you.