Reminds me of dealing with my girlfriend's ex-boyfriend when they were dating and we all worked at the same place.
Her ex was REALLY abusive toward everyone around him, calling them foul names and generally insulting people at every chance. He would even go so far as to tell his (then) girlfriend that she "sucks the joy out of everything". (Which I do not understand, since she is one of the most wonderful individuals I have had the priviledge of knowing)
Until he tried that sh*t with me, that is. Unlike everyone else there, I wasn't intimidated by him, and responded not with nervous, placating laughter, but with unmitigated hostility and threats of violence!
He started being nice to me real quick.
Same thing with terrorist thugs. Treat them with kid gloves, and it only encourages them to escalate their atrocities. But let them know in no uncertain terms that their sh*t WILL NOT be tolerated any further, and they scurry back to the filthy holes from whence they came.