Mothers' Day/Fathers' Day
Certainly when I was growing up (in the UK), Mother's Day/Father's Day were for your mother/father (and, perhaps, your grandparents), they weren't for other mothers/fathers in your life. I think this is still broadly the case for my British relatives/friends.
Whereas the Americans I encounter often see it as important for, say, you to celebrate your husband - and not in a helping the children to celebrate him kind of way, for you to sign a Father's Day card, buy him gifts from you kind of way - and, more generally, for you to celebrate Mothers/Fathers in and around your life. For instance, there's a thread here which asks "which dad should I celebrate?" and the OP is trying to decide whether she should spend Father's Day with her dad or her husband.
Maybe I'm out of step with what happens in the UK (I don't have children) but, if we had a child, I would expect my husband to help the child to make a card or whatever but I wouldn't expect him to make an effort to celebrate me, I'd expect him to do that for his mother. I'd do the same for him. It wouldn't even occur to me to have as a dilemma whether I should spend Father's Day with my dad or my husband - one is my dad and the other is not! Obviously, the former would win.
Is this a transatlantic difference or have I just made it up?