It'd be hard to say what I'd do. Obviously I'd be devastated but I don't think I'd get angry unless 1) the person tried to leave or 2) they refused to apologize. It's amazing how many people would simply drive away rather take responsibility for what they've done. It's also amazing that me, a 22 yr old, is the one saying this. I'd expect even more maturity from someone older.

Good luck getting it fixed! Those new techniques that shops use are there for a reason. Better service and better results.