The "this is a girl's thing, you don't belong" is in his head. There is a colour that he feels threatens him because of its perceived "femaleness", because in the mind of misogynist men (most men are at least slightly and mostly unconsciously misogynist, doesn't make them bad people, only vehicles of the patriarchy), purple = female, female = weak, therefore men + purple = weak because female.

It's another challenge, true. But it's not a challenge he is going to face out of this group on a much worse basis than women in the medical system, who see their pain systematically downplayed and ignored even in the case of an emergency. He is being treated by the medical system as though he was a women, aka faking it and less worthy of being treated, but instead of addressing it with the medical system, he turns it into a pity party in a support group with "what about my menz feelz????" type of tirade. He will find empathy here for when he feels betrayed and sees his struggles ignored by the medical system. Yes, he may feel emasculated when doctors tell him he can't have fibromyalgia because it's a women thing. But nobody here told him that, nobody here treated him badly for being a man, and we are all open to discuss problems in the medical system, the fact that it takes time to be diagnosed because of the invisible nature of this illness and the bias that it is an old woman thing (yes, most doctors believe you can't get fibromyalgia if you are not in your 40s, despite cases of children of 10 or less years old developing it). He is not unwelcome at all to talk about the male experience of fibromyalgia, but he thinks he is because of a goddamn colour and the fact that he is a minority in the group, and that's his problem, not ours.