I'm going to tell my potential roommate that her boyfriend is not allowed in our house
Why are you so adamant about banning him from the house?
I think he is a moron and needs to stop ruining things for others.
You should talk with your roommate about his behavior. If you can't work something out you should find a new place to rent.
That sounds like the best solution.
Maybe she could talk to him. If he respects her opinion and is open to acting on constructive criticism, you should give him a chance.