Sap

This meaning of the word is related to the military process of undermining a wall: figuratively related to “stealthy or insidious methods of attacking or destroying something” (228). Walters (301) notes that the word is used as a mild form of abuse in a friendly, jocular manner. The word is derived from the French word sappe, shovel (266).

Context: 
Well done, you sly old sap
Opera: 
Act: 
Act II