Bad Drivers - "You shall not pass"

Sorry for borrowing a quote from Gandalf.

I don't understand the driver mentality that seems to run rampant in metropolitan areas where many drivers simply don't like being passed.

Taken to its extreme people will engage in an accelerating, lane blocking, and traveling under the speed limit game just to annoy you - simply because you tried to pass them.  Or, more common than this - that they thought you might pass them.

Today I was in a two lane left turn lane that merges into one after about 1/8th of a mile.  This is a well traveled commuter route and its well known that one lane is used by people that want to drive the speed limit or better (I live in an area that travels through somewhat rural areas and some folks do drive slower than the speed limit).  I sensed that the driver next to me might be a slow poke, so I got in the other lane.  I accelerated at a pace that my Honda civic would allow in order to stay ahead of it.  Well, this person didn't like this one bit - they accelerated after  I was ahead and gunned their engine to slip in front.  Then they decided to halt this when they reached 5mph under the 50mph speed limit.  They continued at this speed for the next 3 miles until the road ended and when I slowed to 40 behind them to see if they would pick up the pace, they slowed down to 40 as well.  This forced me to get closer to them just because I didn't want to travel 10mph under the speed limit (you can not pass on this road).

Now, in the grand scheme of things although it annoyed me it didn't change my day - but what is going through this persons mind?  Why do they care?  I see this kind of thing all the time.  Some people simply don't like being passed.

Is this some kind of bizarre inferiority complex?  Do they think we are trying to send a message by passing them?  When eventually I passed this person I looked to see if perhaps it was a young guy - to my surprise it was an older female (mid-late 30's I'd say).  She didn't seem to be paying much attention to anything but the road - hard to believe she had any conscious knowledge that she annoyed another driver.  So what made her do it?  It was clearly intentional - she really didn't want to be passed, but she was a slow driver.  I have seen this often.