Coming from London, nearly 30 years ago, some of the Kiwi English mangling that I find difficult to live with:
Women pronounced woman – apparently some kind of ethnic empathetic mispronounciation, which appears to have become increasingly popular (particularly amongst left leaning socialists) over the past 20 years.
If it was consistent men would be man. Difficult to listen-to as the term ‘woman’ also refers to womankind (as does man to mankind), which to my ear diminishingly refers to women by their sex rather than as a group.
‘Known’ pronounced ‘know-en’, and ‘shown’ as ‘show-en’, where did that extra ‘e’ come from – perhaps from a need to embellish what is otherwise a relatively clipped English pronounciation.
Debut – of French origin, which is pronounced in English as in the French (‘daybyou’) but without the accent – in NZ is being pronounced ‘dayboo’, strangely inconsistent with the almost correctly pronounced ‘debutante’, rather than ‘daybootant’, which it would be if the pronounciation was consistent.
Dates missing prepositions, so ‘two December’ or ‘December two’, instead of ‘the second of 
December’ – which is probably borrowed from watching too much American TV, although even Americans more often seem to speak the correct form.
Prices, particularly in advertisements, where NZ$999, for example, instead of being announced as ‘nine hundred and ninety nine dollars’ becomes ‘nine ninety nine’, which by English convention would be referring to NZ$9.99. Pretty big shock when it comes to purchase!
‘Great buying’ (the inflected verb) when referring to a bargain item, rather than the adjectival phrase, ‘a great buy’.
Others such as ‘darta’ instead of ‘dayta’, for data, or ‘pro-ject’ instead of ‘proh-ject’, don’t seem so bad for some reason, although I think its a shame when American English pronounciation is adopted rather than British English.
‘Harass’ with emphasis on second syllable, for which there should be no emphasis, apparently a black American affectation, increasingly adopted in England (who also watch too much American TV) and by most Kiwis.
Schedule is ‘shedul’ in English, with ‘skedul’ being an American derived mispronounciation.
Anthony is pronounced an-tony in English not anth-ony. Some people it seems are even mispronouncing their own name!
‘Yum’ as an exclamation of tastiness, which is kind of short form of the babyish ‘yummy for my tummy’. Goo goo gah! Perhaps those that use this exclamation do indeed have immature palates.
Recently we seem to be hearing the word ‘learnings’ on the radio, which should of course be ‘lessons’, as in ‘what lessons did you learn’. There is no singular English noun ‘a learning’, so there cannot be a plural. Not sure if ‘learnings’ is creeping-in as another ethnic empathetic mispronounciation, or ignorance of the English language, or empathy with the ignorant, or indeed all of the above.
.. and now ‘trainings’. Same comments as above. Seems like in sports speak it’s ok to be an ignoramus.
‘Homewares’ is in your face when you visit a leading NZ retail outlet chain. Could they really not afford to correct the signage. The plural of homeware is of course homeware, similarly software, courseware etc.
‘Feed’ instead of ‘meal’ is perhaps another ethnic misuse of English. As a noun ‘a feed’ is used in the context of farm animals not humans.
More generally the Kiwi accent is quite pleasant to listen-to (much more so than Australian), apart from when it engages in extreme vowel throttling (which for some reason seems to be more prevalent amongst females – ‘the woman’!). Erosion of language (whether English, Maori, or something else) due to increasing ignorance, or worse still mimicking the ignorant, has got to be a socially retrogressive phenomenon. Quite different from extension, or enrichment of languages to reflect new or changed concepts.