my dad has got this weird habbit of putting finger in nostrillss?

he has this habbit from very beginning like when I was a small child but now this habbit has become too much whenever he is working on laptop he is using left hand finger for taking out the stuff or just fingering nostril , he does same while reading newspaper, watching tv, talking with me, I am so irritated with his habbit I told him to stop it because it doesnt look good n I say everyday but he doesn't listen n scolds me by saying mind your own business please help me how should I make him leave this bad habbit, I am very serious want advice and no nonsense please