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8.
A phrase used to express apathy towards another's disapproval. Probably one of the most overused and annoying phrases of the year 2011 and will be for 2012. Although it has reason behind it in most cases (mainly when it really is only a matter of opinion) in some cases it does not (when reason comes into play).
An acceptable use of the phrase:

Sam: You look weird as a brunette.

Sandy: Haters gonna hate.

An unacceptable use of the phrase:

Sam: Justin Bieber can't sing and looks like a 12 year old girl.

Sandy: Haters gonna hate.
by mainlyachocolatepinecone February 05, 2012
 
9.
What people say when caught in the act of doing something ludicrously stupid or otherwise wack.

It implies that the criticism their acts receive is due not to their own stupidity and naffness, but instead to some unexplained enmity on the part of whoever points it out.
Cornell is walking along the street with a set of clunky gold caps on his teeth, rendering himself almost unable to speak.

Bystander: What the fuck is that idiot doing with those pieces of metal in his mouth?

Cornell: Haters gonna hate

Bystander: Wait - now your trousers have fallen down completely!

Cornell: Haters gonna hate, fule, haters gonna hate
by Pipe Downn June 12, 2011
 
10.
Mantra for those unwilling or unable to accept any kind of criticism, or simply too mentally deficient to come up with an articulate response
...Insert any entirely valid criticism here...

Haters gonna hate
by fingers76 August 01, 2011