Out of control
I think it must be worth concentrating on why such an event may happen rather than how one thumps a customer!
All of us Instructors are familiar with the phenomenon that students suffer bouts of deafness when under instruction. We know why - it is call overload. All of us are guilty of overloading our students from time to time. Whirlybird to quote; "but he was concentrating too hard to even hear me". Thats it, in a nutshell.
The T/F chap asked to take over the Collective "as well" but note; not instead of the Cyclic. Wouldn't we normally demonstrate one control at a time to a student and allow them to practice one control at a time and for good reason. By giving a novice a reasoned structured path into a situation you also at the same time give them a structured way out. This chap maybe had no reverse way out - the structure wasn't in place. He was lost!
The procedure of handing and taking over; "I have control vs you have control" was developed because the need for a structure was well understood. I like the one about 'tickling the nose' i'm sure it is as effective as an elbow in the face. You simply need to break the chap out of the groove that he has been put in - but it is not their fault, they have not joined this flight to be "elbowed in the face".