One from my memory banks.
Puma HC1 in the seventies. Start up, taxy off the ramp to the taxiway for take off. Engage autopilot and lift off into the hover. The aircraft pitches forward so I pull back the cyclic to level it. It pitches even more nose down and I have to pull in loads of collective to keep it clear of the ground. Just as we were about to charge into the scenery I tell myself the the cyclic control is reversed. I push forward on the cyclic and the aircraft responses by trying to zoom into space. There then follows a frantic ten or fifteen seconds where I learn to fly this thing with the for and aft control reversed. It is then in a reasonable hover and I place it back on the ground and shut it down.
The reason was finger trouble during an autopilot repair. The connections on a plug had been soldered incorrectly so the up signal was going to the down pin on the fore/aft servo and vice versa. After the engineers had spent several hours discussing the problem I was told, quite firmly, that I would avoided the panic if I had disconnected the autopilot.
I wish I had had the time to think of that.