Be careful if you shoot or kill a VengeSim because it always attacks the player who last killed it.
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.