PMSL at the last paragraph of your opening post Pixi!
I know how you feel
I have the 'disadvantage' of coming from South London but being (shock horror!) fairly well-spoken. All to often conversations with new acquaintances, especially in the workplace, go like this
'So where are you from ng?'
'Brixton'.
'You don't sound like a girl from Brixton!'
On one occasion, at a business dinner party many years ago, I took the bait. I went to Primary school with a mixed ethnic crowd and many were still friends and I can, or at least could, do a mean Jamaican accent (though not as good as the beautiful real thing).
I replied in a slow Jamaican drawl,
'Well, wha' yoou wan' me to sound like? Ya tink me should sound like dis, don't it?'
As my Jamaican friend and colleague across the table collapsed in tears of laughter the shocked middle aged business man backed off so quickly, I thought he was going to have a heart attack.
he also quickly took his hand from where it had been under the table and on my leg, slowly working its way up, but not before I'd kicked his ankle!
Mr owner of the very posh and well known wine merchant, if you are ever to read this, you know who you are, and you've been outed!