I had a first hand experience of the Serbian character when crossing their border from Montenegro in mid August last year. The custom officers harassed me to pay 180 euros for unnecessary green card insurance and they stripped my car down looking for something "suspicious". They held me there for five+ hours, insulted me and humiliated me without any provocation from my side.
I have a Croatian friend who had told me about his torture by the Serbs when he was caught by them during the 90s. So I made sure I followed their requests and I kept my mouth shut as they were absolutely no other witnesses at the check point. It was five of them against me. They were just bitter and twisted for no good reason. Later on I wrote to their Interior ministry to file a complaint but I received absolutely no response whatsoever.
A lot of other people I know have reported similar experience when passing through Serbian check points.
The Serbs invented and popularized the awful Chalga music that is now dominant in the Balkans.
Croats, on the other hand, a completely different type of people. Even the Montenegrins are different from the Serbs and more pleasant.
As I have heard it from Serbians themselves, they say: We are born fucked in head!
I think you are a bit too much on this. I have passed through Serbian customs many times in my life and never been mistreated.
Serbs and Montenegrins are almost the same people , most of Montenegrins are Serbs. They are just a bit more relaxed and laid-back because they are bigger "peasants" (in a sense that they are closer to agriculture and a bit less educated).
I think you just met the wrong policemen , a lot of them can be crooked , and they can be elsewhere in Balkans. Maybe you were originating from a country with history of feuds with Serbia ?
One thing you must understand is that Serbs are part of the Eastern civilisation somehow , despite being christians. They ve got a certain aggressive behaviour which you only find in many Muslim countries , coupled with the rudeness of slavic soul.
PS : Of course the Interior Ministry won't answer for that , unfortunately.