Have you ever done something really stupid and later looked back with horror? How about these? http://www.gophergas.com/funstuff/womenlivelonger2.htm
The guy with the metal ladder in the swimming pool whilst holding an electric drill gets it for me. His ladder could get some nasty rust. Fool.
Top drawer, that last one really did look like risky, you have to credit the ingenuity though, I think most blokes have made some DIY bad moves, still they always seem like a good idea at the time.
I've actually done the ladder in the digger bucket one. Like you say, it seemed like a good idea at the time