8) Ralph Wiggum (The Simpsons)
Once upon a time in The Simpsons' history, Ralph Wiggum was nothing more than a background character, eventually working his way up to a level of semi-prominence as an inside joke among devoted fans. A funny malapropism here, a non-sequitur about his cat there—life was good... until the second Ralph-centric episode "This Little Wiggy." His appearances shortly after became regular to the point of being painful. Those famous one-liners spotlighting Ralph's stupidity had the zing taken right out of them. Now, there's no more laughs to be had—just the sound of rolling eyes and bitter sighs.