Kara's 'Idol' Nemesis -- It Was All an Act 1/16/2010 2:05 AM PT

Andrew Fenlon -- the "smartass" Kara DioGuardi ripped into and threatened to spank on "American Idol" -- now says his d-bag demeanor was just for kicks.

The bespectacled brat called into The Morning MIX with Scott McKenzie at MIX 105.1 in Orlando yesterday where he said he acted like an ass so he would stand out more ... and get some prime TV time.

Fenlon also claims he would have made it to Hollywood if he would have played it straight for the judges -- so check out his audition, which is replayed during the interview, and tell us ...