I don't know how it got to be different, but in the US, it is mm/dd/yyyy. Sorry, I hate to break it to you, but we didn't do that solely to irritate Europeans. Despite what you think, we do occassionally institute practices and policies for reasons other than to thumb our noses at you.

And who's to say you're right? Over 50% of the world's population, Asia, say it's yyyy/mm/dd. Are you doing that just to piss the Chinese off?