What does Acts 23:2 mean?

The Roman tribune has brought Paul before the Sanhedrin, the Jewish ruling council, to ask them why a mob attacked Paul in the temple. Unfortunately, the tribune loses control of the situation the moment Paul opens his mouth.

Paul will welcome any opportunity to tell fellow Jews about Jesus; and he's going to take advantage of this meeting with the rulers of his people. He starts by insisting on his innocence before God (Acts 23:1). The Sanhedrin knows who he is: a devout Jew with great zeal for the Law who converted to Christianity (Acts 9:1–2). So, the high priest has Paul struck for his impudence.

Paul responds by calling the man who gave the order a "whitewashed wall." Either because he doesn't know who is currently serving as high priest, or because his vision is poor, Paul doesn't realize the man behind the attack is the high priest (Acts 23:3–4). When he finds out, he sarcastically apologizes, saying, "You shall not speak evil of a ruler of your people" (Acts 23:5).

It's possible Paul is being sarcastic because of Ananias' reputation as a particularly corrupt high priest. He steals tithes meant for lower-ranking priests and uses violence, including assassinations, to get what he wants. Here, as yet another example, he has Paul struck before convicting him of a crime.

The priest Ananias, who served from AD 47 to 58, is the son of Nedebaeus. He is not the husband of Sapphira (Acts 5:1–11) nor the disciple in Damascus who brought Paul to Christ (Acts 9:10–19).