I agree that it's best to give mowers lots and lots of room. There's nothing wrong with riding on the grass! The ability to go off road or occasionally pop up on a sidewalk is, to me, one of the great advantages of riding a bike vs. driving a car in the city.

You can also simply stop for 15 seconds and let him move on. It won't make you late to work, I promise.

The lawn maintenance guy that you really want to watch out for is the guy with the leaf blower. I usually shield that side of my face with my hand, so the grit doesn't get in my eyes.