Near / close to the bone / knuckle

Language or behaviour that borders on the indecent is sometimes described as a bit close to the bone or knuckle. The 'bone' version dates from the mid-19th century and is related to ‘to the bone’ which is very much older, dating from the 14th century, and means to the very extremity, as in 'cut to the bone' because with a knife or a sword one can rarely go further than the bone. Near or close to the knuckle dates from a little later than the 'bone' version, from the late 19th century