Bitter Lake gets my vote both because it's a terrible movie, and because it's a serious movie based on a patently ludicrous concept.
So the plot of the movie is that some kind of generic medieval kingdom is riven by civil war and twelve years in, everything's about to go to shit for the four provinces if they can't make peace like right now. It's about twenty or so minutes of boring peace talks, five minutes of would-be romance scene, seven to ten minutes of paranoid whodunnit after they start getting killed off, and two or three minutes of the bad guy describing his plan in elaborate detail to the assassin, who was working for him all along. My favorite part has to be that the bad guy is the brother of the main character, who gets one mention in the movie as being "retarded" and then he's completely forgotten about until the end, when he shows up and he's just all "I was never really retarded, my brother was just a cock".
Now, the concept that's so terrible is that this is a furry movie. It was performed entirely in full fursuits; I checked out the website afterwards and it didn't mention if the cameraman or any of the rest of the production crew wore fursuits while they were working on the movie, so I'm forced to assume they did. But the upshot of all this is that the faces are almost completely immobile. The mouths open and close in a rather pathetic parody of talking, but beyond that there's no expression whatsoever, so the actors are all just hamming up the body language in a desperate attempt to sell the lackluster vocals.
It was all really kind of terribly hilarious.
