Much as I don't love Helen, I do believe this. Brian is weird, he did have a very murderous and out of control look on his face. He also did often have tantrums and that is just what we were shown.
He was odd in BB8 too. Wetting the bed, mooning over the girls, dribbling when he spoke.
He seems to take himself very seriously and then gets frustrated whilst struggling to get his words out or make a coherent point. This then leads to his rage.
And yes, Harry seems to have kept herself dressed all the time he was in the house, but that could have been Helen or Nikki rather than Brian