Before the bandwagon rolls in and claims racism and nationalism i'll say to you now; 'fuck off'.
Anyway, i and my clan/friends get banned off German servers more than anything, whether it be commenting on their shambolic gameplay or just getting the kills in and outplaying their clan on their server, and they'll look for any excuse to get the bans in. They just seem like poor losers more than any other nationality. That said, i've played on some awesome German servers run by some very fine German players, but the bias is more towards the pathetic nature of some German clans.
Probably second in line is the British servers, and i'm a Brit , it's actually quite a close tie tbh.