Passing through Missouri (somewhere near or past Springfield, I believe) on the way to Illinois, I witnessed a semi-truck whose driver decided it was a great idea to wait until the last second to change lanes on the highway, while another driver in a Hyundai Sonata was attempting to legally pass him in the left-hand lane. He then proceeded to make an obscene gesture out of his window for approx. half a mile, then leaned on his horn when the Sonata managed to pass him. Several miles later, after deliberately speeding just to catch up to the other driver, the man repeated his offensive actions toward the cars driver, all of which I noticed because I was following the semi-truck in order to obtain the details of the truck drivers license plate.