Evidently, this UK carpenter did not get the message.

The court that tried Ashley James Humphries likened the incident to a bad comedy sketch, but there was nothing funny about what happened when he jokingly tapped a coworker with a cordless nail gun. It fired and sent a nail into the coworker's leg just above the knee, narrowly missing the femoral artery. The victim required surgery under general anesthesia and is currently unable to work. Humphries had brought the gun indoors to warm it up over lunch break and claims not to have known it contained nails or a battery. He admitted to police that he had behaved recklessly and that it was an idiotic thing to do.

You'll get no argument from me about either.