How about the roomie who swore she knew exactly how to build a loft and nearly killed herself, my kitties and me in the process?
I admitted at the time and to this day to having no idea how this was supposed to work, but it seemed silly to have a mattress on the floor and no space for a desk in my apartment bedroom. So when Vicki suggested we build a loft it sounded great.
Saw, saw, hammer, hammer, well into the night. Hoist my mattress and boxspring on top and climb up. Vicki climbs up too, and starts moving around to ensure it'll hold up to whatever might happen up there.
Suddenly and yet incredibly slowly, the mattress began shifting horizontally. We looked at each other in horror, utterly helpless to stop what happened next. Then, BOOM! Having shifted as far to the side as the planking could handle, we dropped about five feet to the floor. Planks broken and aiming every which way, I took about a half-second to see if she was okay before leaping up to look for kitties.
Smart kitties. They'd avoided the bedroom since the hammering began. They probably thought we were insane, and the were right to think so.
When I described Vicki's loft design to a friend, he offered to help build one that would actually hold up. All of Vicki's angles had been something resembling 90 degrees (Level? Who has one of THOSE in college?), but my buddy's included a few 45-degree angles he assured me would make the difference. He was right.