In the 1970s it was a requirement for trainee RAF pilots to spend an hour in the ATC tower every month and sign a log as having done so (v. good idea, in my view).
The Jet Provost's r/t system made both pilots' microphones "live" whenever either transmit button was pressed so you had to be careful not to "butt in" from the other seat.
One day we heard a student call: "MAYDAY.... MAYDAY....
PRACTICE MAYDAY!"
Immediately followed in the same transmission by "You
IDIOT!" from his instructor.
All the air traffickers jumped a foot, then hooted with laughter!