Most of us don't mind how people speak with regional accents, but sometimes it is fun to mock those who make a deliberate and sudden change because they perceive that they would otherwise be victims of discrimination. One of the famous ways to to this is something called the Giggleswick-trap or Giggleswick-test, named after a place in Yorkshire.
A pre-existing and well known test was 'Love, Mother, Honey, Bus', but it is too familiar to potential victims and a practised dissembler would already have rehearsed it to perfection.
If you want a better one, this Giggleswick Test is to be read, sight-unseen, by the suspected culprit:
"Oh, blast! The brass strap that fastens the glass in my Dad's gas-mask has snapped; the glass has cracked, and my Dad's mad."
Northerners or Southerners who are comfortable in their accents will have no problem reading this, but pretenders will have to calculate, for each word, how much to tighten the vowel. The word 'strap' is the first to make them pause, and then 'snapped', 'cracked' and 'mad' will probably get them too.
Do you have similar tests where you live? Please share.
Small note: I never did like that use of the word 'mad'! Perhaps it is not northern enough?