Ditto some Australian accents. I once met a man from Australia, couldn't understand 90% of what he said--and I was told he was speaking English. Of course he probably couldn't understand me either.
Australianese can be handled by me, if I really turn my ear to it (I was in the Aussie lobster importing business and have spent time there).
But there was one evening in Perth a few years ago, where I was really jet-lagged and it was a company party going on....they mumbled their slang to each other, and I felt pretty lost.
...and the West Aussies speak as distinct a lingo from the Easterners as in the U.S. - just takes awhile for us to pick up the differences.