guy 1: dude, yesterday i put on some iron maiden and just started to headbang bj  guy 2: i really need to try that
listening to metal and headbanging while your penis is in your mouth
"guy 1: dude, yesterday i put on some iron maiden and just started to headbang bj  guy 2: i really need to try that" What is the definition of "headbang bj"?