@Warma-Sheen It's also about playing games though. Something about them makes people go from "it's only a game" to "these people are only players, and thus part of the game so who cares". I can't quite explain it.
And it's not just video games, not at all. At my old job I was playing basketball with these guys... you couldn't find nicer people. Family men with kids, long-time professionals, polite to others, considerate, well educated - a bunch of us were MScs and PhDs... the works. Then we'd go play pick-up games (or worse, real games in a stupid league for businesses) and you'd see them turn into these crybabies whining about every call, disputing fouls, throwing balls around in disgust (one smashed his phone on the floor, his wife wasn't greatly pleased about that)... it was really bizarre.
Couple that with some anonymity, unaccountability and the fact people who're quite shy and uncharismatic in real life can be the center of attention like they always craved and weird things happen online.