Racial slurs while fixing a car

This incident occurred on January 23: 

On Monday, my father-in-law was fixing his car headlights in our condo community parking lot. He was approached by one of the neighbors who began yelling and cursing, accusing him of leaving trash on “his” lawn (mind you it is a community greenbelt). My wife’s father kindly advised that there was nothing littered, but the neighbor continued spewing racial slurs and yell, “go back to your country you f*cking dog!” Apparently, this fine gentleman even took his time to find my in-law's Facebook profile and has been sending him aggressive messages. It’s a sad to see that a simple argument (that, to my knowledge, was unwarranted) comes to this. He has harassed me at work via phone and email with similar racial slurs.