When trying to correct a flight path excursion, the pilot would find his controls frozen leading to brief, hilarous moments. Only in this case, the pilot (now operating under a different SOP) did not correct the flight path excursion with the control column, but by adding a little downwards trim. A few seconds later the captain noticed that this did not have the desired effect, so added more trim. And more. And more. The passenger, seeing that his practical joke did not fly, decided at this point in time to remove the gust lock.
The results were horrendous. The aircraft all of a sudden pitched down with something like minus 1 or minus 2 gs. Both the captain and the passenger, which were not properly strapped in, were smashed against the ceiling of the cockpit. In the cabin the result was even more dramatic, with several cabin crew and passengers breaking limbs and getting cut.
Cracked me up, anyway.