Rumors have been circulating around the internet for the past decade or so of an episode of Dexter's Lab that was never shown on air - it allegedly featured the main characters swearing like sailors.
Called "Dexter's Rude Removal," It was kept under pretty heavy lock and key, and apparently only shown once or twice at cons. Well, until they decided to go ahead and release the video on the adult swim youtube channel.
It's worth a watch if you've got 10 minutes or so. SFW.
Edited, Jan 22nd 2013 8:59pm by IDrownFish