“Cretans are always liars”
As one of their own prophets has said, 'Cretans are always liars, evil beasts, lazy gluttons.' (Titus 1:12 BSB)
What it sounds like today
A startling ethnic insult sitting in the Bible.
The cultural key
Paul is quoting Epimenides of Crete, the semi-legendary poet-prophet (the same figure behind 'in him we live and move' at Athens, Acts 17:28), and the joke was already old: a Cretan declaring all Cretans liars is the liar paradox that Greek logicians chewed on for centuries. Crete's reputation was proverbial enough that Greek coined kretizein, 'to Crete,' meaning to lie. Paul cites the line as a local witness ('a prophet of their own... this testimony is true') about the island's notorious deceivers troubling the churches, with a lawyer's wink at using their own prophet against them.
Recovered meaning
Not ethnography but courtroom technique: when charging Cretan troublemakers, call a Cretan authority as your witness. The paradox is part of the flourish, and the instruction that follows is practical: rebuke them so they become sound.