Who you make your booty calls to. A friend with benefits.
"Last night, Becky called at 2 am and asked me to come over. I guess I am now her official bang buddy."
a best friend or a booty call; buddy with benefits.
All my bang buddies are my best friends, we like to bang!
Girl: Did your girlfriend tell you she's my bang buddy?
Girl: Jus' sayin.