abydocomist
A liar or sycophant who boasts of his falsehood.
archaic
Falstaff: "I may lie, but I am no counterfeit." (paraphrased)
The character Sir John Falstaff from Shakespeare's plays (Henry IV Part 1, Henry IV Part 2, Henry V, and The Merry Wives of Windsor) is a famous example of an abydocomist.
Where it comes from
From Ancient Greek Ἀβυδοκόμης (Abudokómēs), after the town Ἄβυδος (Ábudos, “Abydos”), the inhabitants of which were known for inventing slanders and boasting of them.
Adapted from the Wiktionary entry abydocomist (CC BY-SA 4.0).