VengeSims hold grudges; they target the last player who killed them, whether or not the player was a teammate who may have done it accidentally. If it kills its target, it plays as a normal simulant until it is killed once more. It is then scripted to dash to its target, shooting anyone out of the way.
Dispose of them as you would any simulant. If you don't want it attacking you, maybe you should try not killing it. It's worth a try.
Or you can use their ruthless behavior for your benefit. Try battling a team of VengeSims and 'bait' them to kill each other by 'accident'. This might cause them to in-fight with each other since their lust for vengeance doesn't spare allies or friends. This can be a humorous or beneficial tactic to use!