Why?

Why oh why do some people insist on driving on the bloody line if they see you splitting lanes? It's not like it's by accident either as you can see when approaching that they do it on purpose. And why do some try and see how close they can pass you once the traffic opens up? This morning on Barry Hertzog a chop in black Range Rover tried to see how close he can pass me at whilst I was doing 80kph and him probably 120kph and as soon as he passed he cut in front of me.