Slowly but surely, New Zealand English is becoming American English, something that is happening to almost all other 'Englishes'. This is what I call 'cultural hegemony', and part of it is Hollywood, and TV - and of course advertising, part of it is simply economic hegemony, and then of course, there's Microsoft Word!
Some of it dates back to the 1940s, but some is more recent.
Today, people use Americanisms they would never have used in previous years. On the news last week, Brigadier General Jerry Mateparai said, about the employment of fantasist Wilce "Dumb decisions were made". Leaving out the passive mood (used in this case for evasion of responsibility), I have to say, "No, Sir. Stupid decisions were made".
Now it seems , dumb means stupid, and smart means clever. But how many people realise that using dumb as a synonym for stupid is offensive to people with disabilities that render them unable to speak?
Calling people 'dumb' when you mean stupid, is a truly 'dumb' thing to do. It makes me think of school yard bullies, dancing around the kid with cerebral palsy and chanting "dummy' at her. Or a shop assistant talking to a carer with a person in a wheel chair and asking in the tone she'd use with a small child "And what would she like, dear?"
She would like you to ask her, and not assume that because she has had a stroke that she is either mute or stupid!
I spoke to my students about this on Friday.
"Some people say "dumb and smart" but those words have other meanings, especially in the Englishes used outside New Zealand and the USA. So to avoid misunderstanding, you must use "stupid" and "clever".
(I also warned them that if they ask for the "bathroom" that there's a 60% chance they will be shown to a room with a shower in it, especially as they all intend to go to countries other than the USA... But that's another story.)