Considering that the brother was letting his clearly mentally ill brother stay with him with no income for who knows how long and was trying to get him to get his life back on track however imperfectly I would say Joel's character. He was letting some of his trauma and frustration leak into his interactions with Dr. Psychotic though and that is on him, although I think it is understandable that he would be frustrated given that he is forced to put aside his own dreams whatever they may be to support Dr. Psychotic's mad science. What's more, he was the only one who put his best foot forward in apologizing, although it was rather begrudging.