I still can't believe why only the technical aspects are put in this topic. Especially when some users abuse a network, it should be the social aspects that stop the bad behaviour.
Of course this is a technical forum, but that doesn't mean that soft skills/social skills are less important when running a network.
Again, first thing I would do is have a chat with the abusers and make absolutely clear that they are violating rules and that the consequences could imply loosing their network account for longer or shorter period of time. In a paid job this could imply that they can not do their job due to their own fault. Which would mean that they will get a reduction on their paycheck.
In a school situation this could imply that they can't do their homework and get graded with a zero for a project....
At least don't get in the corner of the guy with the problem. THEY are having a problem and they should know they have a problem when they refuse to obey the rules.