Sorry but pressure washer would not get the spray paint off . the only way to get this off is to sand it off then prime it and repaint it, if you were to paint over it that would not work either as it would bleed through as it is black.
But I can understand you not wanting your 61/2 to see the words that were sprayed on it but did you not say that you saw it in his drive-way that is how you knew it happen before you saw it on the road? So do you think that maybe he moved it there so your child or any other child in the neighborhood would not see it. Where do you what him to put it until he can have it fixed. How do we know that he has not already called to have an estimate on getting it fixed but hoping that maybe his insurance will cover it. From what I understand this happen over the week-end. I.m sorry to hear that you are so fast a judging people, for there lack of regard for other people when this was something he didn't ask or want to happen. But the lack of regard should point at the group that took upon them-self to show all of us how small there vocabulary is.
I bet I can say that any parent out there that has teens that go to school with some of these kids can tell you who they are and were they live it just takes the parent to ask. Because I bet it was talked about in the halls at school today. And I can also bet you that those responsible bragged about it.