The phrase 'happy days' is one of a number of phrases to be banned from use in British primary schools along with 'boys and girls', which is clearly no longer relevant since so many children now identify as something other than the archaic concepts of boys or girls.

A primary school head teacher told FNN:

Happy Days is one of those popular phrases that have crept into common usage either from the military or the Fonz. It has been popular with the military as a comment on drone strikes on Afghan civilians and of course the Fonz was the star of the TV show called 'Happy Days'. 

But this kind of talk is certain to foster potential mental health issues for children, since later in life they will face days that are not happy and will find such realities 'problematic'. Better to say 'A happy rather than unhappy day' to acknowledge that not all days are happy.

This and other phrases such as 'get-in' and 'up for it' with their obvious sexual connotations and 'result!', which clearly rewards the idea of competition that is not a valid life skill in today's world since it implies that you won and someone else lost.

Bill "Battler" Heslop commented:

Instead of f**king about with what kids say, just spend more time encouraging them to be nicer to one another. That's what I call happy days.

Hey Muriel! Fetch me a tinny. I'm parched!