mediocrity

People interested in words always point out that mediocrity doesn't mean quite what its main root would indicate: Why doesn't it describe something that's right in the middle of the pack, exactly what you would expect? Instead the words mediocrity and mediocre always suggest disappointment. A mediocre play is one you wish you hadn't wasted an evening on, and the mediocre actor in it should probably find another profession. A person can even be called a mediocrity, though it isn't very nice and you'd never do it to his face.