Need advice on neighbor that threatens people who park in front of his house in the public right of way

Question - My next door neighbor has installed no parking signs in front of his house in the area of the street that is public right of way(we live on the North End). I have limited parking and when I host dinner parties or have guests over, he will sit in his yard and yell at anyone who tries to park on the street in front of his house in a really threatening way. Again, the street in front of his house belongs to the city and is public right of way. No other neighbors on our street do anything like this. I wouldn't have such an issue with it if he hasn't verbally accosted and scared multiple member of my family and friends for just parking! I find it to be unneighborly and frustrating. What should I do?