rotten to the core

: having rotted : putrid

: morally corrupt

: extremely unpleasant or inferior

: to an extreme degree

: a central and often foundational part usually distinct from the enveloping part by a difference in nature : such as

: the usually inedible central part of some fruits (such as a pineapple)

: the place in a nuclear reactor where fission (see ¹fission 3) occurs

: to remove a core (see ¹core 1a) from

: a group of people