That sucks, although your parents should have done a better job respecting their neighbor's dog.
Mrs Redfoot kept letting our dog shit in our neighbor's yard, and one day I walked out onto the deck and stepped right in a pile of dog shit on the welcome mat. Neighbor must have gotten pissed off, picked up some shit and laid the trap. Mrs Redfoot was super pissed at the guy. I thought it was a shitty way to handle a grievance, but I wasn't too pissed because our dog was shitting in his yard and he has kids and whatnot.
I'm not equating the two situations; poisoning a dog is way worse than putting shit on a deck.
That said, it did ruin a pair of sweet corduroy ugg slippers that they don't make anymore.