Can't claim it to be the most rubbish but the lyrics of "Give Me Everything Tonight" by NeYo are jaw droppingly bad
The lyrics to quite a few songs are quite bad. If you search "ADoseOfBuckley" on Youtube you will find quite a few musical autopsies, dissecting lyrics up.
An example of one autopsy is here: http://www.youtube.com/watch?v=lyrxaFORQXA
(Lorde - Royals)