With some little boy in blue
Who don't know you like I do
--
Why don't? Does it have any secret content?
Song: Elliott Smith - Between The Bars
Don't in the third person is very common in many non-standard varieties of English round the world. Popular songs often make use of these varieties.
There are many dialects of English that conjugate both the to do verb and the to be verb "incorrectly." In my extended family, I often hear all of the following:
He don't
We wasn't
You wasn't
When I was quite young, I removed these from my idiolect, because I wanted to speak in a higher register. The lyrics of this song may simply be written in the songwriter's natural dialect or may be purposely used to give the impression of writing in a specific dialect.
Songs!
They use 'different English' if not bad!
In songs, it is common. One of my favorite songs too has it. Check here: https://www.azlyrics.com/lyrics/michaeljackson/whoisit.html
She don't....she don't... is heard many times. As the answer here says, it's lyrical English and everything is fair there!