Note 1 at 1Co 4:9: The apostles were not really last in any sense of the word. In this same epistle, Paul said that God set the apostles first in authority in the church (1Co 12:28).

Paul was using sarcasm and irony to convict the Corinthians. In the previous verse, Paul said they had exalted themselves and their opinion as if they were somebody special (see note 5 at 1Co 4:8). Here he was sarcastically following their line of thinking and speaking of the apostles as if they were nothing.

It is hard for us to get the full impact of what is being said without a little knowledge of the Roman barbarisms of the day. In the morning, gladiators were summoned to fight to the death, but they wore armor to protect themselves. However, at noon, the vilest of people were put forth to fight to the death completely naked without any protection. Even the one who won was condemned to fight again so that death was certain. These individuals were spoken of as "doomed to death," and this is the literal meaning of the Greek word "EPITHANATIOS" that was translated "appointed to death" here (Strong's Concordance).

Paul was saying that they had treated him as a doomed man in the Roman theater. They had made a spectacle of him. They were professing themselves to be wiser than Paul, making him a fool in comparison. They perceived themselves to be stronger and more honorable than Paul (2Co 10:10).

He sarcastically used his circumstances at the time (1Co 4:11-13) of being hungry, thirsty, without adequate clothing, etc., to help make their point that they were better than him.

Of course, this would have brought conviction to the Corinthians to hear the one who brought them the Gospel speak of himself in these terms, so Paul said in 1Co 4:14 that this was not done to shame them but to bring them to their senses.

The Translator's Handbook interprets Paul's statements this way: "Paul's language is...ironical. He means, 'If you look at the way we live, you would not think that we apostles are the most important among the church's leaders.'"