It's tough to top the "mowed down by a Bayliner" incident, but mine came last fall at the H-16 North Americans in Rhode Island.
Over 40 years of sailing without a serious incident, my crew gets tangled up in a pitchpole - and held underwater as the boat went turtle for what was probably the longest 10 to 20 seconds of either of our lives. I could see her head about a foot below the water, but couldn't pull her free.
That freaked me out. Just the thought of having her drown so close to the surface.
Of course, she did come free, got her head above water and gulped down a lot of fresh air. I still had to cut her leg free from the jib traveller line wrapped around it to get her loose.