Why did Mick refuse to wear anything but a black shirt and camouflage pants to church in the novel, Mick Harte Was Here?

When Mick learned that he was seen in church in a christening gown, which he likened to a lady's nightwear, he refused to wear anything to church after that but a black shirt and camouflage pants, an outfit that spoke to the idea that Mick had only masculine and no feminine qualities.