It is not Possible That There will be Any Surprises.
There is a comprehensive “do not” list in place to protect the well-being of all passengers and ensure that the aircraft travels from point A to point B as quickly as is humanly possible. It is unavoidable that passengers who disagree with this policy will routinely act in a manner that is contrary to the established protocols on board.
Regardless of how crafty these passengers may believe they are, the cabin crew has extensive experience flying and is aware of exactly what they should be looking for. It is not a good idea to sit in the bathroom and do nothing, including not taking your pants off.