If we are going to be honest on this forum, we must readily admit that we have probably never even heard of the worst movies of all time. All the films you are speaking of are _Citizen Kane_ compared some low budget, independent movies. Here are some indie Horror films that were painful to sit through. (The reason I have seen these is because I am a sick individual that enjoys movies like this-they can be funny if looked at with the correct frame of mind...this was a long parenthetical.)

1) CrakerJack'd(sp?)- about four "Homies" that refuse to let a "Cracker" into their "Crizib" for a party that was "Off the Heezee." He comes back and kills them. Some of it was funny, but mostly disgusting innuendo. (Really disgusting.)
2) Driller Killer- this was pathetic. I could have shot something better than this and put together a better soundtrack. As one might guess from the title, a crazy man kills people with a drill. The box said that it was a bit like _Taxi Driver_. After seeing the movie and re-reading that statement I feel like vomiting.
3) The Invisible Maniac- now this was a winner. One of the best of the worst. It was about a science teacher that can become invisible with his special "serum." He then proceeds to watch the high school girls shower and kill the boys. Side Note: if you need some soft core porn but don't want people to know it's porn, rent this.
4) Bloodfeast 2- the crowned jewel of these films. Funny, Bloody and plenty of "used to climb the rope in gym class-esque" moments. If you can get a hold of a copy, do it. You won't regret it...ever.