I want to be your backdoor man
The endeavor of sodomizing an active partner or a person to whom which you're affiliated with in a sexual bond. A pre-eminent phrase originally used by Led Zeppelin's Front-man - Robert Plant - in their track "Whole Lotta Love".
girl: "I really like you, but is there anything you would like to share with me before we do it...?"
guy: " I want to be your backdoor man..."
girl: "...."
guy: " I want to be your backdoor man..."
girl: "...."