As Salamu 'Alaykum,
“When you hear God’s revelations disbelieved in and mocked at, do not sit with them until they enter into some other discourse; surely then you would be like them.” (4:140)
The main way to deal with a violent person is to stay calm. Although many people recommend assuming passive and submissive body language: eye looking down, hands unclenched, jaw relaxed. However, I personally think it is important to make clear that you will not tolerate abuse or violence. Should the person become violent with you, file a police report and follow through. No one has the right to threaten or harm you. (OR, you could do like someone I know did in the case of a violent husband who broke her foot in five places, tore her lip off her mouth, and removed the cast when she returned home. Leave the person, file for a restraining order, start dating your friends brother/sister who is a martial arts instructor and have him/her handle it and buy a gun. ( But I wouldn't recommend this. It is best to let the professionals hand it. ) If the police won't take action than go to an organization that deals with victims of violence and get their help.
Was Salam