This doesn't count because it sort of did turn into a big deal but this one time I fudged up an order of business cards. My boss asked me to change the phone number on the design, and I misread his writing and typed the number in wrong. I sent the design to him for approval and he okayed it and I went and had them ordered. That was his bad, it was his writing that was weird and when I had him double check it he didn't pay attention. But then when the mistake was caught and I fixed it, for some stupid reason I didn't delete the older typo'd version. I kept both. Guess which one I sent off to the printing company? It was a $100 mistake and boy did I get a lecture for that one