About 7 years ago I was flying an RJ. A middle aged UPS captain asked for a ride up front. We of course granted it. Once out on the taxiway the airport was closed for departing traffic and we were told to shut down. For another 1 hour we were beat to death with his complaining about how it was utterly insane that UPS only paid him $225,000.00 a year base pay. After listening to him for much too long I pointed to my new hire FO and said to him "do you have any idea how much she makes?" He said "no" and I told him "about $18,000 base" His response took the cake when he said "Well why would you work here?" and then went on about how expensive his kids private school was. Some guys just don't have a clue.
That's when you "sterile up" the flight deck.
Reminds me of a Airways FO who caught a ride on my plane and insisted that his flight kit ride in the cockpit an that we "ask for shortcuts" so he can get there quicker. I told him that hs kit can not ride up front and he was pretty (deleted)
Seems like most issues come from mainline guys jumpseating on regionals.