A few non-ranty thoughts about 'Griefers'. (a slang term used to describe a player in a multiplayer video game who plays the game simply to cause grief to other players through harassment.)
Griefing, has many parallels to bullying and verbal assault. Most griefers will stay within the letter of the law, (but ignore the spirit of it), which makes it difficult for authority figures to intervene decisively. It is not uncommon for victims to feel that calling for help shows weakness.
Griefers attack people's self identity, their pride, their values. Like an angry drunk at the bar, spoiling for a fight, they'll play nice long enough to ingratiate themselves with a target, and then, bit by bit, turn nasty. Most often, they rely on small subtle comments that provoke over-reactions from their intended target.
The goal, usually, is to make the confrontation seem to be the victim's fault.
Often the victim will pick up on this tactic and fight back even harder trying to take the high ground in a battle where they've already been knocked off balance emotionally. The more the victim cares, the harder they struggle to 'win' the conflict, the more they expose tender targets for the griefer to hit... and, ultimately, the more hopeless the situation becomes for the victim.
Griefing is almost a martial art in its own right, requiring balance, focus, objectivity, practice, discipline, knowing your opponents weaknesses and exploiting them, etc, etc.
Recognize the signs of a potential griefer early. When they bait you with taunts, ignore them or laugh them off by agreeing in a jovial self-deprecating way.
Only a master of articulate wit has a chance of one-up-ing a griefer sufficiently to win a battle, but the war is still lost. The griefer, having found a worthy opponent, will return and attempt new gambits.
Engage in combat with a griefer at all, and they win. They've made you play their game, not your own. Even if you one-up them until dawn, they've hijacked your focus, your concentration, your time and effort for however long the conflict took place.
The only way to 'win' against a griefer is to recognize that their jibes and taunts for what they are, and disregard them. Unless, of course, you're spoiling for a fight yourself, in which case, enjoy.