this really made me think, but I'd have to say... The Garbage Pail Kids! lol that movie was so bad, i couldn't turn it off, i couldn't even look away it was so bad... if you want entertainment and have On-Demand, they have a preview for it on there. It's pretty old and was pretty big back in the 80's.
Barney wasn't intended to be entertaining to anyone over the age of 4, so if you're not still attending pre-school, bashing it is like being from New York and bashing country - it doesn't apply to you anyway.
Anyways, worst movie I've seen in a while would be Pulse. I have such horrible luck with horror movies, I always see the really sucky ones.