Grand Theft Auto games aren't immensely challenging - the game is designed to basically serve up an entire city as your own personal playground, so long as you don't mind stealing cars all the time and murdering every person in sight. But some people like to add a little challenge spice to the GTA stew by doing the impossible - actually following the law. No stealing cars, no murdering civilians, and - hell - even obey the traffic lights. It ain't always easy, but you'll appreciate what you got a whole lot more when you aren't punching a guy out of his own car to get it.
Half the point of GTA games is that there is no point. They're referred to as 'sandbox games' for a reason - it's a huge sandbox designed to let you do whatever you want in it. And, for a lot of people, 'whatever you want' happens to be 'make a huge mess of things' - just like kids in an actual sandbox, except with rocket launchers and a sociopathic disregard for all life.
After nearly 200,000 votes (and lots and lots of comments about Dokapon Kingdom, which we owe an honorary shout-out to), you've decided the top 10 games that tore apart friendships like tissue paper. While some games incredibly did not make the cut, there's no denying that the games that did make it were built to test the limits of good sportsmanship and test relationships in ways that would make Erik Lehnsherr and Charles Xavier piss their pants. Somehow I think those two would have split apart a lot sooner if they had to play Portal 2's co-op mode together.
10. Marvel vs. Capcom (series)
Well, it makes sense that if the worlds of Marvel and Capcom can't get along, why should you and your friends be able to? While the series pits the two universes against each other, they usually come together in the end to defeat some big bad (and totally cheap) mega-villain. Too bad the same couldn't be said for the friendships that were torn asunder by this game, such as when Darren was button-mashing and picking Cable LIKE A COWARD.