Bring on the Insults
"The ancient circum-Mediterraneans had to deal with the stereotypical judgments that were thrown at them. Their strategy was not a doubt about or rejection of stereotypical judgment... They were forced to massage the negative judgments into a positive image that they would want to project." (John Pilch, RBL review of J. Albert Harrill's Slaves in the New Testament)
That, Pilch tells us, was the ongoing cultural preoccupation in a world of stereotypes: turning invective to one's advantage. Paul is an example of such machismo; he was good at pressing shameful liabilities into honorable service. At Corinth he was accused of weakness -- of having a weak presence (II Cor 10:10) -- and instead of denying it, he boasted about it (11:30), implying that through his weakness the macho virtues of endurance, strength of resolve, and courage were demonstrated in the long run (11:23b-27).
This phenomenon relates, as Pilch notes, to the anti-introspective character of the Mediterraneans: since no one but God could read Paul's heart (not even Paul himself), the apostle would have simply accepted what his opponents said about him -- but then twist it to his advantage by incorporating the shame into a positive image overall. Which he did quite well.