I can say the same about Germans. And the French, and Swedes, and the English, and Romanians, and Greeks, and Czechs, and the Spanish...
I have alot of experiance of Polish players as a leader of my guild, and ive had to kick alot of them becouse of their behavior.
Just as well, i could say the perfect opposite, as i've had an occassion to play with nice people of all the aforementioned nationalities.
It's all down to specific personae, and i'm actually quite surprised that such a big part of GW2 community - visible in GW2Guru - is prejudiced based on stereotypes or some previous encounters. My heart bleeds because of it. It really does.
Thing is - the bigger the group, the more jerks it has. It's true to everyone and everywhere, and it's even observable in the community of GW2G itself, when compared to the one from two years ago.