Driving Etiquette

I'm on a pet peeve kick today. Maybe it's the cold weather but things are getting on my nerves easier than usual. Driving down the highway requires a certain type of etiquette. If you are going to bother to speed up to jump around someone and pass them, proper etiquette would lead one to assume you are going to continue on at that rate of speed... or at least faster than the person you just passed.

Just this morning I was moving along at a fairly good clip. I won't incriminate myself and tell you exactly how fast I was going, but lets just say it was a sight above the posted limit, but in keeping with the traffic around me when this guy in a big old SUV decided I wasn't going fast enough to suit him. So, on a rather busy two-lane highway he sped up and darted around me, narrowly missing confrontation (literally) with an on-coming car in the other lane, and then promptly slowed down once he was in front of me until we were both very much under the speed limit.

Was this just for kicks? I'd like to know. There has to be a reason beyond stupidity for it.