A hatefuck is a specific type of sexual act characterized more by spirit and mood than the logistics of what is actually taking place.
A hatefuck typically includes elements of hostility, resentment, powerful lust, roughness or violence, conquest, temptation, intensity, gratification, and/or humiliation.
In simple terms, a hatefuck occurs when two people hate each other but choose to have sex with each other. Variations may include: one-sided (non-mutual) hatred, temporary hatred (like make-up sex but before the make-up has actually taken hold), mild contentiousness (as opposed to genuine hatred), and feigned hatred (a role-played hatefuck).
There are various reasons that a hatefuck might occur. The two participants might be physically or sexually drawn to each other, despite their rational dislike for each other. They might be enticed by the taboo of being so intimate with an enemy. They might have the intent of expressing dominance ("You hate me, but I was powerful enough to manipulate you into having sex with me"). They might view sex as a means of humiliation ("Your lust for me is uncontrollable, shameful, and humiliating"). They might be enjoying ego gratification ("I am so desirable that even someone who hates me cannot resist me"). They may be sublimating actual physically destructive urges into the physical act of vigorous sex. Finally, they might simply want intense, strenuous sex and find that getting a hate-on first allows this kind of sex to occur more naturally.
Since the human mind, the human heart, and sex are all complex matters, there are no doubt countless more reasons that people hatefuck.
A hatefuck is a mindgame. Some people enjoy mindgames, while others do not. Likewise, some people find the idea of a good hatefuck incredibly erotic, stimulating, and positive, while others find it reprehensible, sleazy, and antithetical to healthy sexuality.