Brad Pitt's close friend is fuming after the actor's son, Maddox Jolie-Pitt, dropped his father's last name in the credits for Angelina Jolie's new movie ... and the friend is pointing the finger squarely at her. Brad's pal tells TMZ ... "It’s…

Brad Pitt and Angelina Jolie's son Maddox Jolie-Pitt appears to be following in his younger siblings' footsteps ... dropping his dad's last name professionally in the credits for his mom's new movie. Maddox worked as an assistant director on…