This really boils down to whether the said pax is doing anything that might endanger the safe conduct of the flight or is doing something that is threatening to other passengers or crew. Recent legislation does cover this but the tact and discretion of CC usually overcomes such nonsense.
If a passenger stoically refuses to switch off any device and CC cannot persuade him /her to do so then the matter is for the A/C commander. If the reason for switching off the electronic device is related to EM interference with A/C systems then it could be argued that the commander may be considered reckless to proceed with the flight - return to gate and all the hassle that entails is probably the correct but least palatable option.
I cannot agree that proceeding with the flight then asking the authorities to 'scare' the perpetrator is an advisable option. The commander is putting him/herself in an difficult position as a complainer. Either there was a real risk to the flight - in which case the commander has acted recklessly in proceeding or, there was no real risk and there is arguably no complaint.
The airline rules are defined in T&C of Carriage. A failure to adhere to these policies is a breach of contract. One remedy is to refuse furture carriage or ownward/return carriage. However, this is a civil matter which would not involve the 'Authorities'.
Frankly, I can't undertand why people can't switch off before boarding. Most PDA/phones now have flight mode which I assume means that they stop searching for a signal ( this is what creates the potential problem) and can be used after take off.
I always read the safety card ( to check A/C type and model -it's amazing how different types vary) and listen the the flight breifing even though I am a former pilot and have several thousand passenger flights behind me. If anyone sitting next to me is reading or not paying attention I usually ask them a few pertinent questions about evacuating the aircraft in the case of emergency. Most have a reasonable idea to start with but if you pose a few 'what if scenarios' they do tend to take notice. Anyone playing with a PDA falls into the complacent ' not paying attention' band and needs to be educated.
Once on a short flight from Edinburgh There was a smell of smoke in the cockpit which necessitated a precuationary return. I was fairly relaxed, partly because I suspected the smell was coming from outside (There had been a huge fire in the city the night before and the prevailing wind was from the east, the direction of take off) and because I had confidnce in the flight crew. Interestingly, looking around I could see a number of white faces - the same ones that had been reading the newspapers during the safety briefing. Says it all doesn't it?