The "bear and lion" "sketch" from the Teletubbies.
http://www.youtube.com/watch?v=7poly4w8800
What's really "so bad it's good" there is the voice acting, especially by the bear - what kinda stupid distorted old witch granny voice is that??
Other than that, the notion of putting something this off and creepy (especially the bear) into a cartoon for babies is so bad, it's legendary. The whole show is so weird and depressing, it's remarkable ;)