lostonearth35 wrote:
Who cares what English teachers think? They make grammar errors all the time themselves, they just pretend not to in class.
Anyway, I've been told that I speak very well. Where I live people mispronounce words all the time because we're supposed to all have a quaint Irish or Scottish accent.

Well...whether you care or not, the OP is confused as to what the English teachers are telling him in the first place.
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But it is true that double negatives are only "incorrect" in two dialects of English, but the two that were elevated to being the standard.: those being standard American English, and the equivalent "received pronunciation" dialect of the UK.
The dialects from which all of those rock, blues, reggae, calypso, folk, and country, songs came from used double negatives.
The rational for banning double negatives is that theyre supposedly "illogical". If you say "I aint got nuthin'" its like multiplying two negative numbers - you get a positive number. So "I aint got nuthin;" means "you have something" which is the opposite of what most folks mean when they say it. But other dialects are not being "illogical". They are just using a different logic: that you have to balance the negative start of the sentence with a negative ending. And indeed in standard Spanish the same rule applies: "No tengo nada" literally means "I don't have nothing", and its a perfectly ok way to say "I don't have anything" in Spanish.