Bang easy links with the word bang tidy but has a different meaning. It is used by males or females to the opposite or same sex. When they see someone who is very attractive or good looking, they use this word to show that they would eaily fuck them right there and now. Or in other cases, someone they could easily imagine fucking.
guy1: "damn that girl is hot"
guy2: "Yeah right, totally bang easy"
or
Girl1: Have you seen that new guy at our school?
Girl2: OMG yeah, bang easy or what?!