What did Paul call the high priest Ananias after he ordered Paul struck on the mouth?

Answer: A whitewashed wall

Paul said, "God will strike you, you whitewashed wall!" (KJV: "thou whited wall"), not knowing he was the high priest.

“At this, the high priest Ananias ordered those standing near Paul to strike him on the mouth. Then Paul said to him, “God will strike you, you whitewashed wall! You sit here to judge me according to the law, yet you yourself violate the law by commanding that I be struck.””— Acts 23:2-3 (BSB)