i'll share more stupid ones.
Bought a double trailer with two ski's on it, put safety chains on, but when chatting with the guy forgot to lock down the coupler, drove it 70 miles and hit the little dip in the road 1/10 of a mile from my house, off it pops, makes all kinds of racket and sparks (neighbor was walking and saw it), and when I stopped it slid all the way under my truck and was wedged in there pretty dam tight. It took 3 of us to pop it out from under the frame, won't be doing that again.
Took my honda out to the ramp last summer with my buddy, didn't winch the ski onto the trailer because back then I had carpet not sliders, the ski usually never moves... well, I hit the cattle guard under the water a little too fast (like 3 mini speed bumps) and the ski goes bounce bounce bounce and was 2/3's off the trailer, my buddy is screaming and running towards me as I slam on the brakes, he runs behind the trailer to hold up the bottom of the ski before it drops. VERY close call. Probably saved me $600 in pump/fiberglass damage.