Builders wrote horrible disablist word on my van.

[ArseholeBuilders]

NC for this. I'm pissed off about this and am fantasising about revenge.
A house a few doors down from mine is being renovated, so there has been a builders van parked outside on the street. The other day I came home for lunch and parked for half an hour before heading back to the office. Our street is difficult to park on and the only space was directly behind their work van, so they way I was parked meant they couldn't open their back doors. That's the way it is on our street, it's very congested with parked cars so you park wherever you can find a space. Also I was parked outside my own bloody house.
Of course they still had access to the side door, but they must have got pissed off at the inconvenience because when I got to work I noticed the word 'spastic' written in large letters I. the dirt on the back of my work van. (Sorry, it is a truly horrible word and one I would never use, and any decent person would say the same) I'm 99% sure it was one of them because I saw them throw me a filthy look when I got out the van, and that word most definitely was not there when I parked as I checked the back to make sure I'd left a couple of feet clear behind me. I really can't imagine any of my neighbours doing that. Most were either at school/work and those who weren't are quiet and pleasant retirees.

If it had been a swear word or a rude drawing it wouldn't seem so bad. It's the fact they used such a vicious word that upset me. their van has no logos or company names on it so I've no idea who they are. I've checked their reg for tax and MOT and they're all up to date.

I should probably let it go, and there's probably not much I can do, but I have to admit I've been daydreaming about getting revenge on those little shits. Any ideas? nothing harmful or illegal of course.

@itsgettingweird
But there lies the problem. You can legislate til the cows come home about what words are not acceptable but you cannot stop people using them. If someone called me the N word, spastic, lesbian or other words to try and insult me I wouldn't give a flying fig, as I am none of those things. If someone called me a fat old woman as an insult I'd be more offended because I am those things, so I would take it as a personal insult.
Kids can be cruel, as you have pointed out. We can punish them as much as possible but we also need to support children who may be on the receiving end of such insults so that they can deal with the ignorance of the other children in a way that empowers them.

WHOEVER wrote that was out of order and is the lowest of the low. You think it was the builders because of how you parked, you know you were in the wrong and stopped the builders from accessing their tools, yes they may be able to get in the side door but if , say, the generator they needed was at the back door they wouldnt be able to get it out. Imagine what you would say about a builder parking his van so close to a disabled persons car that they couldnt get their wheelchair out of the car ! No doubt he would (fairly) be called ever name undar the sun. Double standards me thinks