it means what it means-
HATERS ARE GOING TO HATE
Martin: What the fuck? Dude that game sucks dick.
Joey: Whatever man, haters gon hate.
Also, these people tend to think that themselves, opinions, and their possessions are far more superior than everyone else, and that everyone else is wrong.
Also see: A "Know It All"
Tyrone: Are 'yall serious riite now mayne!? Dis whip handles amazing and wait for these pieces I 'bout to buy.
Dan: Still a piece of shit. Always will be. Go fuck yourself.
Tyrone: 'Yall mayne! Haters gon hate!!