The one where I almost wrote myself off. We were supposed to go there, land, and spend our time answering questions as a static display. While in the hold for our landing they asked us to do a ten minute show as a fill in for an unserviceable A/C.
Not ever having done any low level practice I did not really appreciate how much altitude you could lose doing a roll. I started to get some idea when we were upside down in front of the crowd. We got away with it (someone looks after young pilots) but it scared the wits out of my nav and myself. Got a good lesson without paying too high a price. It impressed the h**l out of one of the pilots from the real aerobatic team who were watching from the ground. They thought it looked quite impressive, little did they know.