An overly religious person who stresses his views onto others whether they like it or not. The difference between a 'jesusbanger' and a person with religion is that a 'jesusbanger' feels that anything conflicting their views should be against the law and states this profusely or takes care of the offense by themself. (See also, 'bible thumper.')
Probably derived from 'gangbanger' as both terms are used to refer to a person or thug who has an overly aggressive personality and certain views which they enforce.
Don't let Jaime come in here during the party. He's a jesusbanger and he's just waiting for an excuse to start something.