Driving pet peeve # 241

One of my favorite (insert sarcasm here) things when driving on the highway happened this evening.  I am driving in the right hand lane.  Correct me if I'm wrong, but this is the appropriate lane to be in if you are not passing a car.  All of a sudden I look in my rear view mirror and there is a car that is quickly approaching behind me.  And then it begins to ride slightly closer than I want it to.  There is no one in the passing lane, but this car continues to follow closely.  A mile or so later, as I'm about to merge onto a new highway, the highway adds a new lane.  As soon as I get into the right lane (so now there are three lanes) the car continues in the middle lane and passes me very quickly.  Not a huge deal, but why didn't the car just pass me two miles back when it had every opportunity to do so?  Silly car!