Every game seems to have one country that is generally "bad".
On Lineage II it's Russians. They steal, they cheat, they hack and are generally big assholes towards everyone.
On Ragnarok Online and Maple Story, it's Malaysians, they cheat, hack, behave like assholes, ruins the game and have terrible English to boot.
On Tibia, apparently Brazillians are the ones who are generally "bad". But I don't believe this has to do with their culture or country, I believe it has to do with popularity. Tibia seems to be very popular in Brazil, and thus it attracts a big audience in said country, and thus it also attracts lots of kids and generally immature people who run around going "HUASHUASHUASUHAUSHUSAUHS" while trolling everyone simply because it makes them feel like they're the "King".
I don't know as much about Brazil as I would like, but my theory is that the school system in said country is not as strict when it comes to bullying, and thus many kids in Brazil get bullied, which makes them take out their frustration and pain in Tibia instead, ruining the game for others in an attempt at "bullying back". But like said, I don't know.