This is very common inbmy country too, it is majorly found between commercial drivers , the fundamental fact is 95% of these drivers are not educated so they don't have the basic driving skills and ethics because non of them undergo driving school training.
The major cause of the insult or abuse between them is that they very impatient while driving, they just want to get to their destination at all cost, so who ever that cross their tracks either right or wrong they abuse such person, that's set of drivers are the major cause of traffic hold-up.
They are either hypertensive old men or depressed young men that little triggers their anger, they don't just abuse only their fellow drivers but also their passengers in some circumstances.