the term 'spitebomb' meant
to multiply downvote a post on a website which uses up/downvoting. The spitebombing was usually done because the poster was unpopular (and often by a clique
of attention-whores bearing a private grudge).
The term seems
to have originated on the Sparknotes website sometime in 2002.
the term, and the practice, are now regularly seen on other websites.