"You're dobbed on" was a frequent playground retort. But I distinctly recall that nevertheless as a 5 year old, we took great pride in that we didn't dob. I think children's playground culture has a lot in common with criminal gang culture...
I remember more a "I'm dobbing" said with a distinct whine in the voice.
And I don't mean that Australians necessarily think that dobbing is a good thing, it's just the word itself is not pejorative. The Tax Office ran a "Dob in a tax cheat" campaign, but I can't imagine HRMC ever having a "Grass up a benefits scrounger" campaign. That's partly because you can't say "grass" with a Whitehall accent.
When I left New York after living there for four years (having moved from country Australia), they presented me with a long list of things I said which they had no idea what I meant, but had just been letting go to be polite. Now having been in the UK for over 10 years, my wife still occasionally picks words up (or my five year old son does). Since people often don't tell you, you don't realise the word isn't used here.
Took me quite a while to realise that "root" wasn't an obscenity in the UK, and I've only just sorted pavement/footpath/sidewalk.
(in Australia, footpath is the word for the pedestrian path that runs beside a road, while pavement is the actual surface, usually of the road itself. Yeah, so until quite recently I was very confused by "riding on the pavement", as in "where else? on the grass?")