[onewhippedpuppy]

Car parked on the street with someone sitting in it? Call the cops and report that there's a suspicious car in front of your house. They'll never park there again. As an added bonus, the cops might catch them getting high (likely).

Trash in the yard? Throw it back.

Finally, talk to the owners of the house. If they're as nice as you say, perhaps they'll attempt to reign in the little SOB.

The house next door to me is for sale. I'm a bit worried. Former neighbors were absolutely perfect, with 4 nice boys, one of which was nearly the same age as my son. Fun people to have a beer with, very friendly and laid back.