You should know by now that cops are above the law. They can cut you off, run you off the road, or whatever, there's nothing you can do about it but kiss ass and play to their school-yard-bully egos.

What was the offense he arrested you for?

Edit: and yeah, I've also had many good experiences with SFPD, but have heard that there are a few in the city who are absolute nightmares to cyclists...