If you want your gf to let you bang her in the butt you gotta create her want it as despicable as you do. I started fooling around with my gal's butthole and she kinda liked it cuz it was something fresh and recent after a year or so of ordinary oral and vaginal sex. I wanted to be nice and stuff, but once she got used to my rod being inside of her booty she virtually begged me to bang her harder.