I know "Whatcha gonna do about it?" is a slang term and means "What are you going to do about it" but I'm confused about its meaning in the text below:
At first he watched the younger boys with wary concentration, then he began to bait them. It wasn’t obvious aggression, just small provocations. He might flick off a boy’s hat or knock a soda can from his hand and laugh as the stain spread over the boy’s jeans. If he was challenged—and he usually wasn’t—he would play the part of the ruffian, a hardened “Whatcha gonna do about it?” expression disguising his face. But after, when it was just the two of us, the mask lowered, the bravado peeled off like a breastplate, and he was my brother.
— Educated by Tara Westover
Could you explain if it has a negative (or aggressive) meaning?