Similar thing happened to me in a marina in april in sweden. We had just refuelled and we're doing tick-over back from the pontoon. At that time of the year there were only a couple of boats in the marina.
On one sail boat (approx 30 feet), however, there was a man who started waving, pointing to our 'wash' and shouting at us, calling us f***ing idiots.
Our 'wash' can't have been more than 30 cm max!
Incidently, it was a nice day and a pretty marina, so I had my camcorder out and I managed to get the incident on tape. Maybe I should post it some time.
Mind you, the guy did shut up, once he realised I was filming him!