haters gonna hate ?

The meaning of "haters gonna hate" itself is:
"people who hate others with no valid reason will continue to do so regardless".

The use of this phrase, is usually as a response to the speaker of negative or insulting comments, as an indication that the insulting comments, along with their speaker, are of no value, and can be totally ignored.

Here is an example in the "Urban Dictionary":

*Guy 1 is walking down the street and passes Guy 2*

Guy 2: Why are you so ugly?

Guy 1: Haters Gonna Hate. *Keeps on walking*