I don’t know who is BU here so I thought I’d ask.
I occasionally say to my kids, in a jokey way, that they are behaving like a ‘lunatic’. This is meant as a mild and unserious way of saying they are being silly. Or e.g. I might say ‘come on out now, you loony’ to one of them who is covering their hair/the bathroom floor in bubbles.
My husband feels this is rude and insulting to the children. To me it’s just a word for a silly person (though yes, I am aware of the historical use) and not meant in any literal way.
I do feel that he, and the rest of his family, take themselves massively seriously and that’s not all that helpful at times. On the other hand, I was brought up to communicate in a much less formal (frivolous) way, and it could well be me who’s in the wrong?