The saying "He is as cunning as a Shithouse Rat" is used to refer to someone who is expertly sly and/or sneaky. A shithouse rat being of a lower class than even a regular lowly rat, makes this form of cunning even more underhanded.

This term does not refer to anyone's "mental state".
Don't take your eye off him for a second! He's as cunning as a Shithouse Rat.
by Treasur-Ess February 19, 2016
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Deranged, demented behavior that others deem similar to that of a rodent that dwells in a wood shithouse.
He's crazy as a shithouse rat! If his toes slip off that steering wheel that car's gonna roll.
by Rev Tolby October 17, 2007
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Insane, disturbed, having no control over one's actions.
That guy wearing the ski parka in August, he's crazier than a shithouse rat, keep away from him.
by teh pope December 10, 2004
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A person with exceptional observational skills, as in being able to spot items in complex or busy environments.
That lads got "eyes like a shithouse rat"
by OwDo June 10, 2022
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