Pet Peeve #1 (of 1001)

I was taught in driver education that one should leave at least 1 car length per 10MPH between you and the car in front of you.  When I do that, someone pulls into that space.  Which leads to those who follow you so closely, you cannot even see their headlights in your rear view mirror.  On side roads, this leads me to lower my MPH so that the car behind is at least 1 car length behind me.  Okay, I'm a crochety old woman and you hate me...so do not tailgate.