as cunning as a dunny rat
slang Especially artful, sly, and deceptive. A "dunny" is a toilet, specifically an outhouse. Primarily heard in Australia. You know you can't trust Tim—he's as cunning as a dunny rat. I always thought she was as cunning as a dunny rat, and her manipulative behavior last night proved it. I'm not surprised to hear that Michelle ripped you off—she's always struck me as cunning as a dunny rat.
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