Back in the commuter days I had an relatively mature FO who wasn't dangerous or anything, just a little slower than most. One day this check airman, who had it in for the older guy, comes along for a ride, and in the middle of the flight berates my FO for not saying "thank you" to the controller after getting a clearance direct! The biggest loser, was of course, me, for never telling our chief pilot what a jerk this guy was.