When it feels good to be pissed off, because you're on a self-righteous rant or because you're totally in the right and the other person is an utter nutjob.

Who fucking knows anymore? First, it meant factual, and now it means fictional. What the fuck, internet... what the fuck?

v. To be jealous of another's success or talent. Note that the person being hated on must posess these qualties; thus it is not possible to hate on Ja Rule,Hilary Duff, or Paris Hilton, for example.

The hate version of a hard-on

n. then v. Based on the model of the noun "hard on", a hate on is an active hatred for someone or something that causes a visible physical reaction in a similar fashion that an erection would be a tell-tale sign of affection. Despite its origin, it is rarely used in a sexual context. It is male juvenile slang in the sense that it links, even indirectly, an emotion (hatred, jealousy, envy) to the male teenage obsession with the penis.

to insult or verbally attack someone. originally implied jelousy, now also used for more generally applied abuse.

Can be defined as a very intense professional sports rivalry. derived from the term hard on , as in a very in depth and intensely loving relationship between two people.
watching two teams with a Hate-on is often a very thrilling and hard fought experience,as both will try bring their A game and play their best.