I did threaten to swat any sticky fingers
Firstly, there is no excuse, short of regaining control from a frozen student/pax, for physical actions in the cockpit. That means both from instructors
and students.
The human psyche reacts differently when placed under stress, and announcing an impending situation, rather than inducing one, letting it unfold and observing the student reaction, then debriefing and modifying the behaviour (if required) later, can have two very different outcomes.
Might as well give "Captain" Bloggs a cornflake licence if they think they're too good for training.
I have seen personally a student, who was able to competently complete 45 minutes of successive PFLs, fall apart completely ten minutes later when one came as a surprise.