I only have some annecdotal stories, from a friend who grew up in Croatia and then had to flee during the Yugoslavia war, where one of the parents is Serbian and the other is Albanian. The stories are both from his childhood (being pushed into the sea as a kid, because they noticed he's from a certain group, not being sold bread as a kid because he used the wrong word when ordering) and from recent years (e.g. getting beaten up at a bar by a group of people, because from his accent it was clear he wasn't from that area).

I'm not trying to say that Serbia sucks, or that Serbs suck, or that all Serbs are like that, or anything in that direction. Almost all people I personally know from ex-Yugoslavia (including Serbia) are great people. But – especially given the conflict-rich history of that area – there are still a lot of conflicts and animosities between ethnic groups, and Serbia also has its fair share of xenophobia (in contrast to what GP suggested in their comment).

What's happening is what's happening everywhere else: there are different Serbians, some are great, some are nice, some are not so nice and some are terrible.

Ask Serbs what they think about gypsies, gays, and jews.

Eh, I kind of hoped for at least an attempt to substantiate opinions, but fat chance.