Can't really talk about Science Fiction without talking about the Eye of Argon. Considered by many to be one of the worst piece of writing ever. The author, Jim Theis, tried to destroy every copy ever but was unable to get his hands on the copy published in a magazine.
It's actually a fun activity for people at Science Fiction Conventions to have reading circles of The Eye of Argon. The rules are simple, you read it out loud and pass the story as soon as you start to laugh. The fun part is seeing how many times around the circle it'll go before being read all the way.
I don't think anybody can write this badly on purpose. On the positive side though, you can tell from reading it that Theis made liberal use of his thesaurus. If you haven't read it yet and want a good chuckle, defiantly take a look at it. This story is a real gem of badness.
Here's a link I found online of the story.