I think that the best fail that I have was with the Apple-Cinnamon Pull-apart Bread. I made a double batch and put them into two different 12 inch ovens. At the end, there was this gooey sauce that came from the apples/sugar/cranberries (my addition)/cinnamon mixture. I thought, "Hey, that would be a shame to waste!" So I poured it over the top of the bread in one of the ovens.
Also - this was my first REAL attempt at bread. So I was not yet used to cooking breads. I burned the bottoms, severly. The tops turned out pretty good, but it was IMPOSSIBLE to save the bottom.
Well, in the one oven where I poured all of that yummy gooey goodness, it went beyond burning...the sugars in the stuff BONDED with the patina. It would not scrape out, and when it finally DID come off, the bottom of the oven (in patches) was shiny silver. NOT GOOD.
So that led to my very first re-seasoning ever!
There's my big fail so far...
-Darren