Poor Airmanship? Pilots reading non-relevent material in the cockpit during flight.

[IGh]

Check for one "PF" and one "PM", you to the crew-bunk

GB asks about the difference between a pilot's duties, and a passenger's recreation:

"... the correct, professional protocol about what to do ... in cruise ..."

Maybe there might be one Pilot Flying, and one Pilot Monitoring (if that is defined in your company's regulations). Once you've got that problem solved, then go back to the cabin or to the crew bunk (don't distract the pilots).