I broke my left collarbone when I was five and from then on I became right armed/left handed. I eat and write with my left hand but do almost every thing else with my right.
I used a monocle once. I was in Montana, driving home from work in the dark in a heavy goddamn snowstorm. I think it was the heaviest I saw in the 10 years I lived there.
I had to stop for gas, and while I was pumping, my old '90s big plastic-frame glasses got covered in snow. I got back in the car to wipe them off on my shirt, and the fuckers broke right in half. Like, straight down the nose.
So all I could think to do was hold the broken left side of the glasses, with one lens and one arm, in front of my left eye. I sort of hooked the arm over my ear and touched the broken nosepiece to my face. I closed my right eye, and drove with my right hand. In a goddamn eastern Montana blizzard.
So the answer to the above question is: A monocle should always be worn opposite your driving hand.