Discription of Events: Driver sped up to left lane of minivan and drove closer and closer to minivan, pushing them off onto the shoulder. GMC came 1/2 across into minivan lane while visibly yelling and shaking finger at driver or minvan. I flashed lights several times, worried for the safety of minivan driver. GMC Slowed down substantially to then wave and yell at me as I passed, which I took photos of.