Boyfriend has a temper. What's the best thing to do during an enraged person's outbursts?

I would say to talk to him and tell him how much it frightens you when he does that and maybe see if he would be willing to go to anger management cles or something that could help him learn to get control of his emotions before they get to that out of control point. Things like tempers usually start with emotional stress and get worse over time not better. Try to get him some help to learn better coping strategies. Good luck