I don't have a top 5 worst list, I see too many bad movies and it becomes hard to differentiate one from the other. But, I recently saw Uninvited, and the last 5 minutes were just so mind boggling bad, it makes it worth a rental. The entire movie is shit, but with the final scene in the life boat, my IQ dropped on the spot.

http://imdb.com/title/tt0096341/