Check with your local police department, but I doubt there's anything your neighbors could possibly do during daylight hours, as long as the car stays more than 8' from the street. If the local PD confirms this, tell your neighbor that if he (they) threaten (after all, that's what they did) you again, you're going to file a police report. That should shut them up. Use the law to YOUR advantage (sounds impossible, I know, but it's not!)!!
Take care,
~Chris