Actually, I've always frosted my cakes while they're still a bit warm. The frosting kind of melts into the top layer and makes it really soft and gooey. I ruined a cake once by letting it cool too long and it got dry. Maybe it's just me, but warm frosting can work if you're careful.
Remember my friend who tried to frost a chocolate cake straight from the pan? She was in a rush and the whole top layer just peeled right off with the spatula. It looked like a landslide of crumbs and melted frosting. We ended up calling it "chocolate pudding cake" and ate it with spoons. What's the weirdest cake fail you've had to just roll with?