It happens all the time. I was at work and sending a reply to one of my friends and I was talking trash telling him I was going to come down there and kick his ass. Well I didn't reply to my friends email, I accidentally hit reply to a client's email and mistakenly told a client I was going to kick his ass. The kicker is I had only been at this job for a month so I was brand new. Our client called my GM and he came in my office all serious and told me what I had done (i didn't realize it) and I was shitting bricks (sorry shitting rocks). Luckily everyone involved had a sense of humor about it and now I am the butt of a few jokes.