Not my neighbor, but a friend’s neighbor:
Friend is particularly bad about yard care. His grass was always long, and the rabbits happily munched on a buffet of dandelions.
The neighbor (sharing part of the backyard property line) decides he is fed up with this, and sprays Roundup, or something similar, in a two foot wide line all down the property line, on my friend’s side. As expected, everything in that two foot wide swath dies. Guess what grows back in that now vacant patch? Not nice lush grass, but a variety of weeds.
Yes, my friend should have taken better care of his yard, but the neighbor was an idiot 1) for spraying the Roundup in the first place, and 2) for not foreseeing that outcome.