Hard to have a nice yard, when neighbors have a Dandelion Nursery!

2 4 D is cheap (or used to be) and so is a hand pump up 2 gal sprayer. Go over there and spray his yard after he goes to bed, and then in a couple days apologize and say your dog pissed on his whole nasty *** yard and killed them darn yard flowers!
Hit them in the spring before they make those darn seeds! For a couple of years. That will go a long way.