Neighbor is being a jerk during showings for my flip

A lot.  Go meet with him - and the other adjoining neighbors.  Tell them that you're selling the house and that you will let realtors/buyers know that they are to park at your property and not disturb the neighbors.  (And, then do just that with potential buyers; park at your property, do not wander into neighboring yards, respect the neighbors' privacy, limit showing hours to daylight hours). Give the neighbors your card and invite them to call you directly ("don't waste your time on these people, call me").  While some neighbors can be a pain in these circumstances, I have found that the constant "stranger danger" and intrusion into their properties gets very old, very fast.  And, by making the connection and demonstrating respect for their property rights, you'll pick-up some eyes and ears to watch over your investment until it sells.  

Hope this helps.  And, congrats on your flip!