[Advent Calendar 2013] "The Star Wars Holiday Special" (1978)
The rarely-seen Star Wars Holiday Special. Why is it rarely seen, you ask? Mainly because it's hilariously awful. No mere case of FX failure or cheesy dated script, this -- the fact that this has no particular cult following, whereas Shub-Niggurath does, is rather telling. It is the kind of bad that can only be stumbled upon by accident. For the longest time, rumor had it that Carrie Fisher had the only copy, and refused to show it to anyone out of sheer embarrassment. It pops on and off the internet at irregular intervals; judging from the appalling picture quality, this is sourced from someone's ancient VHS tape. Not that a clearer view would make it suck less.
(Hey, it's Friday the 13th. What did you expect?)
For added amusement value, get the thing explained by The Nostalgia Critic.