Sly Dog By EvilMay 21, 2014February 25, 2020Popular Expression “Sly Dog” = a sneaky, devious, or just plain lucky person/ animal. *Often “sly dog” is used as a term of admiration. Ex: You just met her, and you already got her phone number? You “sly dog” you! Ex: You have to be careful because he is a “sly dog.” When we play cards, he is very quiet and sneaky. BACK to Popular Expressions