Dislike thy neighbour

There has recently been a rather unpleasant sight at the entrance of the back garden: a few cigarettes butts on the porch. The main suspects are our next door neighbours: late at night, I have seen a few young adults/old teenagers hanging around the garden, speaking and chatting. At least one of them was smoking. So now I have a legitimate grudge about some of the people living next door. I have been a bit busy recently so I have not confronted my neighbours about this, but I intend to do it, although I do not know the tone I should take. I tend to be rather aggressive with these matters and lack of sleep can make me nastier. My wife tells me to take a diplomatic approach. After all, these are most likely the kids of the house next door, not the adults. All the same, I now officially dislike and distrust my neighbours. Some of them anyway.