Making a physical threat crosses a line, and those people need to be dealt with. As for dealing with the trolls making gas chamber jokes, I'd just stop reading Twitter. Or the Facebook/YouTube comments. Frankly, I don't think reading the yammerings of the unwashed masses on unpaid, unverified social media accounts is some kind of requirement for living a productive life, even when you make your bread through online content. Sorry if it sounds harsh, that's just what I think, and what I'd tell a loved one.