college student rental question

[Bruce Godfrey]

I have a 5-bedroom rental populated with college students and this is my first rental property. The tenants are all friends, but one of them has become difficult. For example, he frequently crosses the line with his "humor", making inappropriate sexual references. He lets his alarm clock go off for hours. He makes aggressive and inappropriate comments to guests of the other room-mates. So he hasn't technically broken the terms of the lease, he is just an unpleasant guy. However, if this continues, a couple people have said they will leave and I know others who have decided not to move in because of his behavior. 

What recourse do I have against him and is there any language I can add to my lease agreement to prevent this in the future?