He see you are getting trouble by a group of people. He save you and kick all of those people away. After they all gone, he look at you and say, "Be careful next time." And just like that, he leave.

You doesn't have a time to say thank you as he gone so fast. You know he is in one college with you. But you also know that he have a reputation as a bad guy there. Some of your friends have remind you to not get close or even talk with him. So, what will you do next?