Never mind = don’t worry, forget it…
«Mum I failed my exam».
» Never mind, you can try again.»
On my mind = something you are worried about…
«The exam has been on my mind.»
Out of my mind = worried, drugged…
«I’ve been out of my mind with worry over the exam.»
Never you mind = for someone else to forget, not worry about something.
» Mum, why did uncle Carlos touch your bottom?»
«Never you mind,» says mum.
To describe personality…