Had one doing that while I was going the same speed as the 10 cars in front of me on the highway during traffic time. He was flashing his lights and when there was an opening on my right he changed lane and then I saw... The guy was in a full size truck and was pulling a 20' trailer and was trying to pass me on the right and squeeze between me and the car in front of me so he would have been stuck behind them instead. I didn't give him enough space, he got back behind me even more angry than before and 3km later reached his exit so he wouldn't have saved a single second if I had let him through.