A story that I told on a similar thread a few years ago:
1986 on a SAA 737 classic. Internal flight from GRJ ~ JNB a simple 90 minute sector. We were pushing back and the safety is started. It transpired that we had a new CC on and it was her first day of actually reading the saftey announcement. A wily fox on the flight deck is waiting to initiate her in a particular tradition ...
"... place the mask over your face and breath normally." At which point, old fox presses his PA button - overriding the CC - and does 'heavy breathing' into the microphone.
It took the poor girl some moments to recover ...