...taxiing out solo in the 152 after forgetting to close the oil hatch on preflight... saw it just short of the holding point, had to shut down and get out to close it...
Did that one too - it wasn't completely closed and popped open at about 100' AGL after takeoff. Instructor calmly kicked in a little rudder and it snapped shut. Learnt a neat trick for future use although I hope to never need it