Yes to both, drivers flaunting the car-free restriction are generally poorly skilled and cyclists on Market are generally quite aggressive.

I do it by riding slowly in front of them and pointing. Their options are to try to swerve left around me and get hit by a bus, jump the curb, or run me over.

I've not tried it in SF, this is me speaking of my experience in Houston.

In SF I'll block cars from making an illegal right by simply standing in front of them.