Definition of one's head is a marley in English:

one's head is a marley

phrase

Northern Irish
informal
  • One is foolish or stupid.

    ‘I love you but your head's a marley’
    • ‘"Catch yourself on, wee girl. Your head's a marley."’
    • ‘"Tony, your head's a marley. Just for once, do the right thing."’
    • ‘Your head's a marley; I could climb it, no bother.’
    • ‘You want me to stay here? Your head's a marley.’
    • ‘"Our teacher's head's a marley; he's put George in for the eleven-plus."’