There is not much you can do when a motorist insults you and then drives past, but for those parking lot encounters, might I suggest this?

Obtain a copy of your state's Motor Vehicle Operator's Guide. Make that TWO copies. Read the section on bicycle safety, and hilight the bullet points describing your road rights.

When confronted, show the offender what the DMV says about your means of transportation.

You can provide that second copy to the disbelievers.

This tactic works very well at the workplace, where every fat, sedentary SUV jockey thinks we should be turning slow circles on bike paths and in mall parking lots on Sunday mornings.