Reprobation means disapproval. Severe disapproval. If you want to find out what it means for yourself, try telling your nasty boss what you really think of him.
Originally reprobation was a religious word meaning "rejection by God." The root word probate comes from the Latin word probare, which means "prove." A probate is someone who proves his worth. A reprobate was someone who'd proved himself to be worthless, and was therefore condemned to eternal suffering in Hell. Pretty harsh, huh? Today, a form of the word can even be used affectionately: "You old reprobate!"