Whites of Their Eyes

“Oops. My bad.”

It’s very easy to make the mistake of not placing a “friend or foe” rider onto a readied action. Saying something like “I attack the next creature to move beside me” or “I put an arrow into the first person that moves” rather than “next hostile creature” or “first enemy”. Most gamemasters are generous enough not to have you kill a party member, but it does happen from time to time. It’s a good way to teach players to be careful what they say.

It’s very justifiable. Combat is a hectic environment and it’s easy to mistake an ally stepping up behind you for a rogue moving in for some back stabbity action.