I let them know I'm there and fill their rear view mirrors with my grill. Then if they don't get the message, I turn on my LED flashers and blind them. If they still don't get the message, I go around them, either the shoulder or the middle lane.
If they're old, I give them some slack as they just don't know any better, but they shouldn't be on the road.
Douchebags who tailgate me and there are no options for them to pass me or for me to move over or speed up because of being trapped around other cars, I let off on the accelerator and have slowed to under 50km until they get the hint.
Ontario has to be the worst for idiot drivers who don't know the rules of the road. Driving in the passing lane, not indicating, common courtesy, etc etc. In Quebec, I've always noticed that almost everyone uses the highway lanes appropriately, unfortunately, they seem to ignore a lot of the stop signs.