How is the sentence "My mama don't like you, but she likes everyone" correct?

I just heard Love yourself by Justin Bieber. I thought I heard "My mama didn't like you but she likes everyone" from the song. Then later I found lyrics on some websites(listed bellow) but it's not what I heard, it was "My mama don't like you...".

Any idea about this?

• http://genius.com/Justin-bieber-love-yourself-lyrics
• http://www.directlyrics.com/justin-bieber-love-yourself-lyrics.html

Usually, (assuming the song or poem is good at grammar), you can determine the tense of the verb by simple contextual clues, but after clicking on one of your links (and, thankfully, having never heard the song) I found that his verbs are all over the place ("you rained on my parade," "you think you broke my heart," "I'll be movin' on"), so I can't tell whether didn't or don't was used without listening to the song, which I am not doing.

Technically, the sentence "My mama don't like you, but she likes everyone" is not grammatically correct; the use of don't instead of doesn't for the third person singular is, in my experience, pretty common slang. Also, "doesn't" has too many syllables. "Didn't" instead of "don't" is correct; it has too many syllables and creates an inconsistent verb tense like the rest of the song.

In other words, it isn't.

Yes, in this case in a song for instance, it has to do with the tempo of the music. If you listen to the Beatles' song 'She's a woman' there's a statement that says

She don't give boys the eye

If you used doesn't it would be longer and the tempo of the music is not enough.

There definitely isn't a "but" there. The lyric is "My mama don't like you and she likes everyone".

In terms of whether it's right or wrong: it's idiomatic usage. Native speakers will understand you.

What it means is his mother is a lovely, friendly person and even this lovely, friendly person doesn't like you which illustrates how bad you are.