There is not much you can do in situations like this, the best thing to do is ignore it and if you want to concentrate on school do that. In my old school there are fights everyday apparently, when someone threatens you to a fight try to ignore them and when they punch you, punch them back. If they say fight after school then its up to you to A: get out sneaky B:just do it. Most people who want to fight after school forget it, the best thing you could do is just move schools if its a REALLY big problem especially when someone threatens to bomb the school