Spite is the desire to harm, hurt, upset, annoy or offend someone else - and it is a terrible sin because it is both insatiable and self-righteous.
A spiteful person sees happiness and wants to destroy it, on the grounds that it is smug, and it will be good-for those concerned to experience a bit of 'real life' - he observes with satisfaction the misery of others because they 'deserve it'.
Spite is worse than Schadenfreude because spite is active - spite is actually going to the trouble of causing trouble - expending effort, time and resources to create suffering in others.
Spite is ignoble, petty, babyish - whereas some people embrace the sin of pride and try to defend it as a good thing; nobody does this with spite, nobody makes a big thing about their own spitefulness - not least because it reveals their dependence on others.
That many of the highest status people in the world are primarily motivated by spite is extremely obvious; although - perhaps because of horror at the reality of this fact - people talk as if this was an extreme and outrageous suggestion. Yet surely our insight and personal experience tells us that spite is nearly universal to some degree; and the dominant passion, the prime motivator, the principal drive and source of energy for a significant number of people - including some of the richest and most famous, the most intelligent and educated, the most charming and beautiful.
Indeed, in my personal encounters with the elite, the mass media stars and celebrities; petty spitefulness is probably the major and most striking feature they seem to share in common.
In sum; it is the spitefulness of an evil person that causes so much trouble for others. A proud spirit damns himself; but it is spite that motivates him to drag others down; it is spite that makes him a nuisance, a wrecker, a ruiner, a destroyer; it is perhaps spite that most distinguishes a demon from the general run of lost souls.
Note: I remember how, as a kid, we especially used to dislike and fear spiteful children. Perhaps especially those pretty, 'perfect' ballet-dancing type girls, the ones whom the adults thought of as especially 'good', and always believed - but whose greatest pleasure seemed to be asserting their superiority with barbed comments and insightful criticisms that you couldn't stop thinking about; and who quietly delighted in getting other children into as much trouble as possible, whenever a safe opportunity arose. And of course there were plenty of boy tormentors too - including the most dominant and 'popular' kid; who would terrorize, or make gangs in order to enjoy the misery of their victims. But, in general, spitefulness caused more childhood misery than almost any other cause - and it was a special bliss, a kind of paradise, to be among any group of kids that was free of such characters.