Repaint my mirror?

do I have to use primmer to repaint my mirror, or can I just paint over bare metal

Self etching primer is what you need. Or else the paint will peel over time. rather quickly too.

definately use primer 1st and lightly sand it afterwards before you shoot your color paint on.

Depends.

If you're painting it a color, like red, blue, green, etc. Then yes, it could be wise to use a etching primer. Then the color and or clear coat.

Now if they're just satin black, like say off a 93' Mustang. Then you may be able to just sand the mirror down, or scuff it with a gray scratch pad if new. Then hit up a auto body supply store and get a can of SEM black bumper trim. This black is a OEM factory black that will match about any satin black found on cars. Mirrors, hitches, wiper arms, trim around doors, etc.

If you must primer, sand with 600 grit then paint.