It's difficult if not impossible to pinpoint a single event as being the trigger for all-out war. I think it was more of a chain of events that escalated.

I personally know Serbs who were driven out of Dubrovnik in 1990. While the hysteria was being propagated by all media in the region (not only Serb) there were also numerous acts of violence perpetrated against individuals. I can't say whether the media was instigating or reacting to real events.