Serbs involved in ethnic-cleansing (& their supporters). The tragedy they committed was horrible. I blacklist such. Even with pure logic, I would not want such bad neighbors/socialization in our communities.
Newsweek cover "hate thy neighbor" was summarizing that. Some Serbs kept their specifics, too. The videos they had shot, and kept circulating among their groups, were publicized in 2006 (or so), showing that the murderers in that sufacing case were the daily-known neighbors.
Besides, the Serb "excuse" was totally absurd. Bosnian muslims are of the same race as Serbs, while people in Kosevo are known to be resident there even before the others. Thus, neither was brought there by Ottomans. The serbs's hatred of centuries, thus, applies to me (living in the old capital of Ottoman state) maybe more than to their victims. If they wanted to keep those victims away, they are supposed not to want to keep in the vicinity of mine, by their instincts, any way.
& I think the Ottoman state was a fair-ruling state. Local bullies may not love, though.