If I had already secured a job,and there was no input from my headmaster in regard to that job, and it was my very last day at the school, I think that I would have told the headmaster politely to go jump in the lake, rather than bend over for a sixer.
My headmaster was a big man, but as a senior, I was no longer a little boy, and I do not see what he could have done if I refused.
I really could not see my headmaster suggesting such a stupid thing to begin with,and by the time I was a senior boy and a prefect, I cannot see myself doing something so childish as setting off the fire alarms anyway.