I was driving north on I-75 leaving Plattsmouth in the left lane and accelerating. I was barely over the speed limit but was in the process of overtaking a car in the right lane when the Honda Civic (who had been speeding in the right lane) abruptly cut me off without warning or a turn signal and merged into the left lane. I immediately braked and honked my horn as the car continued to speed in the left lane before moving over to the slow lane about a half mile ahead. As I continued to gain speed I was attempting to pass the car to then merge over to the right lane, but the car again swerved into the fast lane and then proceeded to slam on his brakes. At that point, the driver was turning around looking at me and gesturing wildly, all the while his car maintained a speed over 75 mph and he continued to swerve into both lanes to prevent me from passing him, making it dangerous for me to be anywhere near him. I was forced to slow to a speed of 50 miles an hour (I was in the right lane by this time) so that I could continue my journey without risking an accident. The driver continued swerving in his car before exiting the highway. I've never experienced an angry driver like that before, nor experienced such unsafe driving conditions from another car intentionally creating them.