If you stiff the Praetorian Guard, be sure to have their replacements lined up and ready...

Explanation: The Praetorian Guard was the bodyguard/secret police of the Emperor during the Roman Empire. As time wore on, they got a reputation for extreme corruption and duplicity, and their history is full of Emperors bribing - or replacing - them in order to secure their own regime. And when an Emperor fails to do either, well, who is better placed than an Emperor's bodyguard to 'remove' him?