Starship Troopers 2
The first was awesome so when i saw a second movie on the shelf at HMV i bought it raced home watched it, it was the largest sack of shite i've ever seen. You know you in trouble when a sequel uses clips from the first movie and the first looks better in every way.
What made it more fun however was a year later at uni when a group of guys on my floor saw i had it and wanted to watch it. I spent 20 minutes trying to talk them out of it but they insisted. 10 minutes after they left the was a knock at the door and when i opened it they where back agreeing that it was shit after just 5 mins of watching, which gave me a hour long laughing fit at their expense.