Acts 23:7

And when he had so said, there arose a dissension between the Pharisees and Sadducees; and the assembly was divided. For the Sadducees say that there is no resurrection, neither angel, nor spirit; but the Pharisees confess both. And there arose a great clamor: and some of the scribes of the Pharisees' part stood up, and strove, saying, We find no evil in this man: and what if a spirit hath spoken to him, or an angel?

Paul's identification of himself as a Pharisee is also offensive to some people; but it should be remembered that the "noble Pharisee" must never be identified with the Pharisees whom Jesus denounced. See my Commentary on Matthew, Matthew 3:7, for classifications of Pharisees. Many priests became Christians (Acts 6:7), most of whom were doubtless Pharisees; and it is very likely that much of Luke's gospel (Luke 9:51-19:28) was researched through Luke's interviews with such Pharisees (then Christians) while Paul suffered the two whole years incarceration in Caesarea. The true and righteous Pharisees, of whom Paul must be reckoned, obeyed the gospel. Paul's words in this passage have the effect of saying, "Only such as I am are the TRUE Pharisees."

The notion that Paul's claiming to be a Pharisee in this situation was improper, is nullified altogether by the fact that he also made the same claim before King Agrippa (Acts 26:5) and in his letter to the Philippians (Philippians 3:5); thus there was nothing unusual about the identification of himself with the Pharisees here.