Originally Posted by FBinNY

Not too bright.

It's legal to ride interstates in some places, but it should be a last choice option. And if doing so, USE THE SHOULDER.

Taking the lane this way creates a compression in the right lane, and there's no reason to assume drivers are alert to you because you're not on the menu of expectations. You had an open lane and saw him at a good distance. But imagine that a car in the right lane, timed a lane change to avoid him at the last minute. That's OK, but now imaging a car following that one fairly closely, and suddenly having this guy right there when the car in between mover to the other lane.

Of course, if you pulled alongside and urged him to find a safer route (even if you did so very politely), he probably would have flipped you the bird, and told folks about obnoxious drivers.