Burning film backwards and not notice until you tape up and start to register screens on press
who does that, me me me me!! 
sorry Darryl, while this is not a competition, I can top that! We actually went ahead and printed the job thinking the backwards screen was background for the art!!!
DUHHHH!
pierre
Well now I don't feel so bad about myself. I left a plate under manual flash unit and took a call... among other things

Steve