Or go visit some websites dedicated to particular TV shows, and look for a shipper flame war.
But... but... Chandler and Ross are just
meant to be, OK?
People in general can get hung up with their interests and take criticism as a personal attack, it's not a phenomenon limited to "RPG guys" or internet users - as has been well demonstrated by the plethora of other examples quoted in this thread.
It's easy to look at a flame war and say "they're only doing that because of the anonymity afforded by the internet, they wouldn't behave like that IRL" - but equally easy to look at film footage of sports-related violence and other extreme "fan behaviour" out in the real world and write the previous assumption off as completely inaccurate. Sadly, people can and do behave as obnoxiously IRL - and oblivious of witnesses, cameras etc - as they do on the "anonymous interweb tubes".
As a geek, biker, gamer, pagan and a number of other things, I've seen "flame wars" on more topics than I care to remember. OS wars - Windows/Mac/Linux, distro wars amongst the Linux set, bikes vs cars, Holden vs Ford, Harley vs Japper, tourer vs cruiser vs dual sport vs crotch rocket, Christianity vs paganism, Wicca vs Asatru and so on.
And you get your more reasoned, moderate people in those areas as well as the frothing-at-the-mouth fanatics - but the fanatics are by far the loudest and most noticeable.
Seriously, short of firing a shotgun into the air and screaming "stop being so extreme or I'll shoot you", it's well nigh impossible for the more moderate person to get noticed at all...