I'm going to leave my trash on my neighbor's property
Why are you so mean to your neighbors?
The shmuck can't even keep his own yard clean.
It's not nice to litter, especially on someone else's property. They might get really mad at you if you do this.
They should clean up their own shit
Adding more trash to an already dirty yard isn't a good solution to them not taking care of things.  You should talk to them about it, or file a complaint, rather than just adding more trash to the yard.