Jamieson, Fausset and Brown on Titus 1:12

12. One--Epimenides of Phæstus, or Gnossus, in Crete, about 600. He was sent for to purify Athens from its pollution occasioned by Cylon. He was regarded as a diviner and prophet. The words here are taken probably from his treatise "concerning oracles." Paul also quotes from two other heathen writers, Aratus (Ac 17:28) and Menander (1Co 15:33), but he does not honor them so far as even to mention their names.

of themselves ... their own--which enhances his authority as a witness. "To Cretanize" was proverbial for to lie: as "to Corinthianize" was for to be dissolute.

alway liars--not merely at times, as every natural man is. Contrast Tit 1:2, "God that cannot lie." They love "fables" (Tit 1:14); even the heathen poets laughed at their lying assertion that they had in their country the sepulchre of Jupiter.

evil beasts--rude, savage, cunning, greedy. Crete was a country without wild beasts. Epimenides' sarcasm was that its human inhabitants supplied the place of wild beasts.

slow bellies--indolent through pampering their bellies. They themselves are called "bellies," for that is the member for which they live (Ro 16:18; Php 3:19).