Can a county cop pull over a state cop?

Yes, although it invites a "ticket war." There was a case last year in the Miami area where a Miami police officer was driving his marked patrol car to an off-duty job, and was moving well over 100 miles per hour. A Florida Highway Patrol trooper stopped him and arrested him. This led to some Miami cops pulling over FHP troopers in retaliation. The better option is to report any bad driving to the officer's employer and handle the situation that way.