badventist
a Seventh Day Adventist who "breaks the rules" of his/her religion by going out or doing things on Friday nights and Saturday before sunset, eating pork and other restricted foods, or just doesn't regularly practice other aspects of the religion.

Basically a combination of the words "bad" and "adventist."
Girl 1: Did you hear about Zachary going to that party on Friday night?

Girl 2: Yeah! He's such a badventist!