if he's upsetting your other posters is that not classified as abuse?
perhaps you can ban him under the guise of 'abuse'.. maybe PM him and suggest he become a serious poster or you will have to remove him from your database
long term you have to pay attention to the people who count on boards, they're the ones making you money - having someone on there who's disruptive to the others and to the general 'feel' of the board can do more damage than you breaking your own 'rules' and banning the guy for abuse
ban him and your other board members will probably feel even more inclined to stick with a board that listens to them
