How naive are you
As Captain Dart said, anyone working in a safety sensitive occupation can be tested under CASA rules. Safety sensitive extends to anyone involved in daily flight operations - pilots, cabin crew, engineers, doctors, flight dispatchers, tug drivers, etc.
Doctors, nurses, train drivers, truck drivers, bus drivers, power workers, so on and so on have been randomly tested for many years in the UK, USA, Australia, NZ.
If you travel in plain clothes you would need to be resident of the destination country or have a visa. PX solves the problem of a visa because you are on the GD.
As VforVENDETTA said, most major airlines do not permit drinking in uniform or part of it - taking your slides, name tag and tie didn't count - you are still in part uniform.