A rat pack is a gang of employees who are allowed to bestow authority upon themselves, and use it to intimidate and manipulate coworkers for personal gain. They traffic in broken spirits; their currency is power.
Rat packs don't just happen, they rise up when managers look the other way too often. They test your authority in little things, then wait. If you look the other way, their tests get bigger and bigger. Before long, they've assumed the power you lack, and begin applying it to their coworkers in the form of bullying and intimidation. As long as you're looking the other way, they're applying their ill-gotten power on those around them. As soon you fix your gaze on them, they become angelic pillars of the workforce.
The more you look the other way---away from dissent, disobedience, and disregard for policies and procedures---the faster and bigger the pack forms and the more power they siphon from you. Wait too long to disband them and they'll convince your manager you have to go.
If you're convinced you have a rat pack in your house, first find the leader. He/she is often gifted at avoiding detection and slick at diverting your suspicion elsewhere, most likely at his/her next target. They're masters at turning you into their accomplice without your even realizing it.
Rat pack leaders are masters at manipulating their managers. It's not uncommon for the leader to accumulate accolades from her superiors. This year's Employee of the Year could be the most feared member of your staff.
To disband the rat pack, all you have to do is convert the leader. She's already proven she has leadership skills. Your job is to refocus them in a positive, constructive direction. Remember, her currency is power. If she can get it legitimately, she'll be just as happy. Change her method of obtaining power from destructive intimidation to team-focused cooperation and the other rats will follow.
But first, you have to stop looking the other way.