Why? Please, please, please can someone explain why?

Why when there is a line of cars driving down the road, the one guy waiting to turn into that road waits until just before the last car is about to pass him and then turns?

In front of me!

When there is not one single car behind me!

Could he not wait the 3.5seconds it would have taken for me to drive past before he turned?

Must he rev his engine and pull into the road right in front of me, forcing me to slam on brakes?

When there are no cars behind me!!!!

Ggggrrrrrrrrraaaaarrrrrgggggghhhhh!