In an earlier comment I mentioned how much I enjoyed this film - better second time around. I don't resile from that opinion. Strangely, I can't find anyone else who did like it.
My mother was going to see it but several friends told her "No way". My sister and her family saw it and half the theatre walked out part-way through.
My wife's suggestion is that Australians see the characters as just normal, everyday Americans and therefore it's not funny. But, hey, most Americans think all Australians are like Crocodile Dundee, so it's nice to have the boot on the other foot for a change.