Assuming you're not trolling; "brigading" is you talk to all your similarly, minded peers on IRC with long-standing, legitimate HN accounts to flag the story because it annoys you. (Different from a voting ring, which may include non-legitimate accounts and lacks the 'tit-for-tat')
I haven't flagged it because it's more than stupid high school drama, it's an object lesson - is the person who would become CEO on the startup team you're joining/funding likely to behave in a similar fashion?
Because CEO Yishan just opened up Reddit to a potentially expensive, but more importantly, distracting lawsuit. It may have saved face in the all important young-male demographic that Reddit caters to, and probably felt good as the CEO to be able to perform to such a public 'smackdown' of a former employee 'running his mouth off', but as as developer it says quite a bit about the the companies culture if the CEO bullies people like that. "Taking the high road" is how professionals act towards other professionals, and while the former employee was far from professional, that might have been the better option for the Reddit CEO to take.
Even waiting a few days to make sure the 'i's were dotted, and 't's were crossed by the legal team, followed by a (short) public blog post refuting the most disparaging remarks made would have been less childish and more responsible would have been better.