a friend/associate's humility index. Two little practical jokes were often used in my flying circles, one in the T-34, the other in the C-172. T-34 Humbler most often used on WA checkpilots or SA others was to take the ship up to altitude, do the mandated maneuvers and then after trimming to cruise, ask the backseater if he would like to demonstrate something or, just fly it for a while. Naturally, what he did not notice was you had turned the pitch trim almost fully forward so that when he says "I got it", you let go of the stick, the acft pitches over abruptly and it tries its darnedest to do an outside loop. (Be sure to turn your intercom volume down!) This also was an excellent way to check how secure the backseater had tightened the harness. We always wore helmets so there was seldom any permanent damage done when the head almost certainly impacted the greenhouse framework. In the C-172, if there was a reason to register your displeasure with something the PIC was doing as he was taxiing, all you had to do was wait until the acft had to come quite close to a parked ship and just as the PIC thinks he has cleared the wingtip or whatever, slide your seat quickly forward and then release the seat release lever. The resulting 'THUMP!' will really get the guy's attention. Also for the C-172, it was not uncommon to have the three pax behave as a team and on a signal unnoticed by the PIC all lean forward nonchalantly. The PIC will roll in some trim to adjust the cruise.... then everyone slowly leans back... and when the PIC rolls in the trim once more, wait a moment and repeat. Usually three or so cycles will do the trick.... Boredom is a deadly factor, ain't it?