I think dialect is the right word?
Anyway, I once really offended a girl who was new to my school. I had made friends with her and she invited me to her house, She got changed and i said 'Omg that suits you dead bad!'. Now, As an adult, I agree with her and can see the stupidity in saying something like that, BUT it was something EVERYONE where i lived said when really what they meant was 'That really suits you'.
She imediately looked hurt and i could tell by the look on her face she thought i was back pedaling as i sort of choked and tried to explain, and stuttered through it. I think she realised within a few weeks when she made more friends though.
My Mum also, after moving to the north, became increasingly frustrated one night. Her partners son came downstairs and asked her (As she was folding laundry) if there were any of his pants in there.
She said 'Yeah there are some over in the other pile'
He went over to look and said he couldn't find any, My mum said there were definitely some in there. He searches again and still can't find any. My mum said 'I just this minute put some red pants of yours in there, i know i did! They must be there'
He says 'I don't have any red pants'
My mum marches over, Grabs a pair of red boxers and says 'Look! red pants! See!'
Only for him to fall about laughing as he had actually meant trousers, and everyone here calls them pants, she just didn't know.