Hey! I know you!
The only two acceptable reasons to do this.
What really pisses me off is when I’m in the middle of 3 lanes doing a respectable 72mph and some jerkweed is bearing down on my right at 80 I know he’s trying to get to pass in front of me when there was plenty of room to pass on the left. If I catch the move in time I’ll speed up to block and force him to go around, but only if I have enough wiggle room.
There is little worse than a smug NorCal Prius driver self-righteously slowing traffic. I have seen that type often on visits out there.