Try pranks-for instance , put fake tickets all over thier car(if they have one.)or put fake eviction notices in thier mailbox,even dead animals on thier lawn. Pranks are so innocent,anyone could have done them ,so they can't really blame you.
Just make sure you don't get caught pranking them tho.
You DON'T HAVE to be violent, you just have to make him THINK YOU ARE. I haven't hurt anyone since 1992... that's when I got my handgun. People's attitudes just seem to magically melt away when they are looking down the barrel of my H&K USP .40, and I've NEVER even had to fire it! The threat of instant death just seems to make people stop "dead" in their tracks, pun definetly intended. My LAST bad neighbor stopped coming by the house, stopped playing the stereo loud, and has done a 180 degree turnaround since I got that gun, mainly because when I got it, I made sure he knew it. I just knocked on his door, waited for him to open it, and when he did, I dropped a handful of bullets on his porch and said calmly "Your stereo is too loud. Turn it down NOW." Then I flashed the gun in my waistband, and walked away. Never had a problem after that. He moved away about 3 months later.