the.com/pot calling the kettle black

means Said of someone who criticizes another for a fault they themselves have, usually worse — accusing while equally guilty.

from From an old kitchen image: both pot and kettle hung over an open fire and ended up coated in the same soot, so the pot was black-bottomed too — making it absurd for it to call the kettle black. The phrase appears in English by the 1600s (it shows up in Cervantes translations and Restoration-era writing), back when cookware actually sat in open flame and picked up that char. Some versions have the pot seeing its own blackness reflected in the kettle's polished copper and mistaking it for the kettle's flaw — a nice twist, though the soot story is the more solid one.