Dealing with greek enemies

Has anybody had an experience with chapter enemies. For example, a person that did not receive a bid from your group, a member of a rival sorority or school, an indepentant, etc. There was this case where a guy who had been turned down by at least one fraternity tried to date two sisters in the same sorority. When he failed, he threatened to call National and tell them that the girls were hazing and making the pledges drink. The girls didn't think much of it, until he did call. There was no hazing or RM violations going on but Nationals did have to investigate the matter and it put a lot of stress on the chapter from Nationals and from the school (the guy went to Student Conduct as well). Does anybody have any suggestions on how to deal with this kind of problem.