Overfly-
The correct word is not "discreetly", it's "surreptitiously." If you were told to turn off electronic devices and you deliberatly didn't comply, shame on you.
Passengers are required to turn off most portable electronic equipment because they may interfere with the comm and nav systems on board the aircraft. In the flight magazine in the seat pocket there is usually a list of devices that you MAY use during flight. If a GPS is allowed by your airline/CAA, then great, have at it. And, there's no need to go sneaking around with it. Since you don't know the flight plan of the aircraft, deviations for weather, etc, you don't know if it's on-course or not.
Bluntly, what part of that don't you guys don't understand? When the Pilot-in-Command and the aviation authority of the country direct you to comply with simple rules that help ensure the safety of the aircaft and passengers, why can't you? As an aviation enthusiast, I should think you would be setting the example, not sneaking around like some schoolboy.