naffairious
Evil/criminal in nature with regards to being unfaithful in a relationship.
Some people occasionally "get a little chocolate on the side" merely for their own personal pleasure, but Slick WIllie's shameless trysts with Monica Blewinskey and countless other trusting colleens were downright naffairious in nature, since they were both so numerous and resulted in such serious fallouts and hurtful repercussions!