As a Denver DUI lawyer, I've seen a lot of crazy situations. This story
from South Africa has to be near the top of the list.
A citizen observed a police vehicle driving erratically. He did the smart thing in calling law enforcement for help. However, after 5 minutes he became impatient and took matters into his own hands. He approached the officer, determined that he was intoxicated, removed the keys from the ignition, and then secured the officer in the back of his own vehicle.
While Colorado law DOES allow for a citizen's arrest, doing so on a police officer is not a good idea. There have been some high profile DUI arrests of law enforcement officers in their patrol cars in Colorado recently but they were done by other police officers. If you are faced with a situation like this, call 911, observe the situation from a safe distance, but DO NOT attempt to arrest a police officer. It will not end well.