Cinema Studies

I am working on my research paper for my class.  It's on the movie Forgetting Sarah Marshall.  It's an offbeat comedy, and a littly odd to categorize.   Is it a Judd Apatow comedy? Is it a screwball comedy?  Is it a romantic comedy?  If its an Apatow, then it's almost a genre by itself.  If it's the latter two, then it's roots trace back to old Hollywood films.    I got my work cut out for me.