Not your standard bristle worm. I'd ditch him. The red ones can be trusted, but I don't know about that one. I've seen similar worms on the reef in Guam and they were quite large. They also made me think twice about snorkeling and swimming without shoes!
It may not be a bad worm, but it's an abnormal worm. That meas that it might cause problems. It also may be benign or even beneficial...but it's not worth the risk in my opinion. Worms can be tricky to find and remove once they settle in.