nincompoop

/ˈnɪnkəmˌpup/
noun
  1. A foolish or stupid person; someone who acts silly or makes poor decisions.
    • He felt like a nincompoop after locking his keys in the car.
    • Don't listen to that nincompoop — he doesn't know what he's talking about.
    • Only a nincompoop would forget their own birthday.
Antonyms