I did something really super embarrassing at work today. I sent an email meant for one person to an entire group of people. It wasn't just a matter of replying to the group instead of to the sender, I actually initiated the message chain and manually typed the wrong address in the To: field. When I realized my mistake my face and neck instantly burned from turning red with embarrassment. I didn't get reprimanded, although I've beaten myself up enough about it that no external punishment short of torture would compare.
So, what's your most embarrassing work story?