backstab fail....

It makes me think of an incident that occured with my group. One of our members was infiltrating a camp and he rolled like a 7 or something so they became aware that their was an enemy in the camp but because he was disguised as one of them they didnt know who. When the alarm went off saying there was an enemy in the ranks in response he turned to the closest enemy...... then decked him while screaming "ITS HIM!". Our DM told him to roll for it and he got a crit 20. So we went with it. Next thing we know a large majority of the camp is in a mosh pit trying to kill this one random guy and we walk away from it.