A worthless witness mocks at justice, and the mouth of the wicked devours iniquity.
Proverbs 19:28 ESV

If someone mocks God's standards of justice, you can't trust him in anything else either. He has already rejected the only solid, objective standard of morality that exists, so you can never even know how he defines truth and honesty. He can explain it to you all day long and you still can't know because his very life is a lie.