Coming from Britain which is tied for first place with France for 'most arrogance per square metre', I and every British person I've ever met has had this. On Ventrilo, I once argued with a guy from the midlands about how the 2hp recovery per second on all these special green level 90 boots were useless and my custom npc boots were better than them. This arguement went on for an hour and a half with no actual result, although I won the arguement because he stopped first.
I also get told every time I complain of a computer issue (graphical lag, loud cpu fan etc) by an American friend that "it's because you have a Packard Bell", I then have to remind him that only the case is made by packard bell, the CPU is ATI, the graphics card is ATI, the motherboard is ATI, the RAM is budget generiram, the PSU is some brand I can't remember, the Hard Drive is generic, the monitor is japanese, the keyboard is microsoft, the mouse is logitek (I think), and he just repeats it's a "packard bell".
I also had this happen:
FriendymcChumbuddy: Are you playing the Dragon Age 2 demo?
Me: It's the full game
Fr: Why'd you buy it it sucks?
Me: I like it, it's fun
Fr: Nope it sucks
FriendymcChumbuddy is now playing Kane & Lynch 2: Dog Days
But I'm just as guilty as other people probably.