If Christ is King, obey the Third Commandment
Ethnic hatred of Jews is wicked and a denial of the image of God in man. Jews are not any more sinful than any other ethnic group.
Way back in the mid 2000's, a spat broke out about the phrase "Merry Christmas." It went back and forth between the Internet and cable news, as people debated the phrase. It quickly escalated to the point where saying "Merry Christmas" was a way to give someone the middle finger. What should be a genuine expression of goodwill became a way for people to demonize each other online. I imagine it would have been much more intense, and much more silly, had social media existed at the time.
I was reminded of that controversy with the discourse over saying "Christ is King." Of course, this is true. It is also true that some people say this not because they believe it, but because they are anti-Semites using the phrase to taunt Jews. Unfortunately, this is part of a growing trend of anti-Semitism on the Right, and U.S. Senator Ted Cruz was right to call it out. (Interestingly enough, the target is almost always Jews, not Muslims or Hindus.)
If you say "Christ is King" because you submit to His Lordship and divine authority, then that is a very good thing to say. Jesus is sovereign over all things, and through His sacrifice we gain forgiveness from God. Continue saying that. However, if you say "Christ is King" purely to taunt people you hate and make them angry, you are violating the Third Commandment. The Lordship of Jesus Christ is something that should be approached and proclaimed with reverence. It should not be said as a way to taunt and troll Jews, and certainly not as a way to encourage ethnic hatred against them.
Christ is King. That is an eternal truth, and we should be thankful that He is sovereign over all things. We should pray that God fulfills His promise in Romans 11:25-29 that Jews will be saved and turn back to the Messiah they rejected, and have faith that He will keep His promises. However, ethnic hatred of Jews is wicked and a denial of the image of God in man. We should remember that we are all worthy of eternal damnation in Hell Fire, and only by God's mercy can we hope to be forgiven. Above all else, the Name of God must never be used for crass taunting. If you do this, repent.