Gangbanging, in this context refers to social media feeding frenzies. Where some poor sap, is caught in some compromising situation or whatever it is, says the wrong thing, is goaded or trolled into making a fool of himself, and everybody piles on. I know it's vulgar but that's the idea. That's the metaphor. And sometimes it gets really wild and vicious. And sometimes people lose their jobs, and get divorced, their personal lives are destroyed in the melee. And that's essentially what happened to BK, all time winningest coach at ND, in case you didn't know. And it was his own fans! And he didn't do anything at all, other than leave ND, and it had been brewing and percolating and festering for years. Before the damn burst, or the volcano erupted, I'll go with the latter. And burst it did, regular twitter-ites were in awe, not even CFB fans, at how vile and sadistic ND fans were being. It lasted several days. BK was trending! And it's been like that ever since.
So you burned that bridge. Or at least your more uncouth and savage brethren did.