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'Honest'? Don't make me laugh.
Literal
Honest [subject-が] hear-[and-て] be-astonished-[assertive-よ].
聞いて呆れる is a fixed sarcastic expression, literally 'to hear and be astonished' — used to mock a claim about someone as being the exact opposite of reality. The structure is typically [word]が聞いて呆れる, personifying the concept itself as the hearer who would be shocked by the false claim. Here: 'If Honesty itself heard you being called honest, it would be appalled.' A very Japanese form of biting sarcasm.