Mayuko is not home and I have no idea what you wrote in Japanese, but I can guess at your question and try to answer.

First, don't forget music and lyrics don't have to worry about grammar as much as sound and rhyming.  So sometimes we have to force the sentence to fit with the music.  No one gives them a grade and no one cares if it is wrong as long as it sounds good.  Same in Japanese I am sure. 

That said, I will look at using a double negative in regular conversation next.

People tend to be lazy and use terrible English in America.  After a long time of that happening, it becomes acceptable and sometimes even becomes a way to add strength to the meaning. 

A double negative is really a positive, but if we are being very casual and trying to really show that we think in the negative we might use it.

Example
A: Do you have $20 I can borrow?
B: No.
A: How about $10?
B: I ain't got NOTHING.

So here, B is trying to tell A that it doesn't matter how low the amount, B will not lend A any money.  This way, A knows not to bother asking about $5.

The phrase "I ain't got nothing" actually means "I have something" but B uses it to stress the negative.  It is incorrect grammatically, but it is also common usage and therefore understood by most people to mean B doesn't have any money.

In the end, I would have to say that it is probably a 50/50 split.  Half of the people are making a mistake and the other half are making a point.

As someone who is not a native speaker of English, you might sounds strange using this or the person to whom you are speaking might think you are making a cute mistake if you try to use the double negative to stress your point.  I remember telling alot of students that if you only have a few really casual, natural phrases and your English is not really good, natural, casual sounding English, then it's probably best to skip the few that you have.

Mayuko sounds great in English, but sometimes when she uses too casual a phrase it sounds funny or unnatural.

my picture here got a haircut.  i am not sure when because i don't always check the site.  i think he looks good.

no, really.  i got a haircut about 2 months ago and thought i should make my picture match.

"Short Cut" is Japanese when you are talking about a haircut.

If you are talking about how to go somewhere and you know a route that is faster then you can say "I know a shortcut" in English.