Ones very experienced friends of mine have admitted to:
Starting a tailwheel aircraft with the throttle wide open. Fast reactions required to prevent the aircraft tipping over.
Starting an aircraft with the bubble canopy unlatched (and shortly after wide open) Jolly lucky it wasn't damaged.
Taxiing with the concrete tie down still attached. I've heard of people who've managed to take off with the tie down attached. Makes you realise what little use the tie downs are.
Taxiing tailwheel aircraft into other ac, ground vehicles, fuel bowsers.
On final approach on a test with the undercarriage warning horn blaring and managing to ignore it until the reds blues greens check- that made the examiner raise an eyebrow.
On the forgetting to strap in one, I flew with a copilot for 3 hours who strapped in but did not realise the straps were not attached to the airframe.
Reaching down to put the ejector seat pins in after a flight only to realise that were never out.
Turning the fuel off in flight and wondering why the engine stopped.
Refuelling and forgetting to put the caps back on. Its amazing how fast the fuel gets sucked out of the tanks once you take off.
All of these happened to very experienced pilots. No number of hours makes you immune - and even a monkey can fall from a tree.