About my scariest was one of my first, as an 11 year-old in 1975.
It happened at Dubrovnik while arriving from Gatwick in a British Airtours 707. It was raining heavily and the approach was bumpy. On "touchdown" some rubber jungle deployed and my mother (who wasn't the happiest flyer at the best of times) pointed frantically out of the window on her side of the aircraft. A nosewheel had detached and was bouncing off into the grass next to the runway. I think at least one main gear tyre was burst also.
I remember reflecting years later that I didn't see the danger in this like I would if it happened today. It says a lot about the safety of aviation that in the following 40 odd years, I've flown hundreds of times (and flown myself for a few hundred hours) and that was the most serious incident I've had.