Develop an Early Warning System

Oftentimes, an early warning system is best developed with the succor of a toxic worker's secretary or executive assistant. 

Because these individuals are best suited to predict rash behavior and/or mood swings. If you're able to successfully enlist individuals in the know, they can be invaluable in terms of alerting you not only of an asshole's presence, but also of his/her daily levels of "asshole-ness."