Drivers' Questionable Actions

I encountered something last night that really made me scratch my head.

I was out for a late night drive, and there was nobody on the road around me. I slowed down because I knew police liked to sit in the area, and I had this Lancer come up on me very quickly. I'm in the middle lane, and so is he. Instead of changing lanes before he gets to me, he speeds right up to my bumper and then changes lanes! The Lancer had all the space in the world and then some, but for some reason got right up my ass before changing lanes. Why on earth would you do that!?

A McLaren F1 LM for your troubles