The 49 year old was in Utah promoting her latest film The Sessions in January (12) when she opted to attend a top industry bash to bond with some of the movie's stars.
But event staffers didn't recognise the Oscar winner and she was forced to head back to her hotel room and rent Katy Perry: Part of Me on Tv.
She tells U.S. Tv host Jay Leno, "(The Sessions) premiered at the Sundance Film Festival... and I had never been to Sundance; I thought of it as where the groovy, young indie kids go - and now I was invited. So I got off the plane, I went to a Hollywood party and was not let in.
"There was a 300 pound bouncer, who did not care about me... He was just not interested. He didn't know who I was. So I left and went home and watched the Katy Perry movie on pay-per-view."