My friend has a room mate whose boyfriend has a vicious chihuahua.?

This dog literally attacks the room mate and my friend as they have bled before from his attacks. He even growls like crazy and my friend and her room mate cannot move from their spot unless they want to be attacked again. My friend has become petrified of the dog and the owner is so oblivious to it all, telling the girls to get over it. What should they do about this vicious dog?