Many sites have a no naming and shaming policy because of the possible legal ramifications which can arise from doing said 'shaming'.
Which is why I didn't mention the dealer, and nor will I on an open forum

If (and I assume from your post this wasn't the case!) the dealer said, "do you want us to wash your car?" and you said, "yes!", then perhaps there would be a grey area as to whether you had asked for a service, they provided it and thus you got charged for it. (I'm playing the Devil's Advocate because even had this been the case, I would think it was extremely poor service to charge you for a car wash! However, in the case above, it could simply be a matter of 'misunderstanding').
Now, setting aside the above, and assuming you didn't ask for the car to be washed or it was never mentioned, then I can understand why you are livid; I would be as well.
At no point did he ask. And as I said before, the car was clean so it wasn't as if it needed to be washed either. Both of my other cars have been in for service recently; both were washed and I wasn't charged for this 'privilege'.
It just annoys me that I've spent over £100 on a car wash - I could have had the car detailed for that!!!