Heard a story once about a barber who shaved a stripe clean across a guy's head... the client ended up liking it and kept the style. Stuff like that happens more than people talk about... makes you feel less alone. Just say sorry and offer a fix or a discount... most people are cool about it. Remember, every haircut is a chance to get better... even the bad ones. Read somewhere that these moments keep you humble... and that's not a bad thing.