"Australian Slang" He was going berko for absolutely no reason!
Sounds a bit like me at 3am when some drunken A/Hole is causing no end of trouble and then wonders why I decide he needs to leave the hostel.
Berko seems to have come from the word berserk which was derived from the Norse warriors the "Berserkas." These Nordic warriors would work themselves into an insane furry prior to battle through a combination of dance /chants/ alcohol and it is thought psychoactive drugs. This would give the warriors an violent blood-lust, great strength and an immunity to pain. For this reason these warriors would continue fighting even when mortally injured or against overwhelming odds.