What is the meaning of “certain women should be struck like gongs”?

In act III of Nöel Coward’s Private Lives, Amanda Prynne tells her ex-husband, Elyot Chase, that she was “brought up to believe that it’s beyond the pale for a man to strike a woman.”
“A very poor tradition”, he replies. “Certain women should be struck regularly, like gongs.”
The marriage between these two character was contentious, and their arguments often became physical. Five years after their divorce, newly reconciled (somewhat), Amanda and Elyot cannot help but bicker every time they speak. At the end of act II, they are interrupted by Victor and Sybil—their new spouses—in the midst of a violent quarrel. When act III begins the next morning, Amanda behaves “as though nothing had happened,” which frustrates Sybil and Elyot. Elyot, characteristically sarcastic and flippant, frustrates everyone.


VICTOR: If you don't stop your damned flippancy, I'll knock your head off.ELYOT: Has it ever struck you that flippancy might cover a very real embarrassment?VICTOR: In a situation such as this, it's in extremely bad taste.ELYOT: No worse than bluster and invective. As a matter of fact, as far as I know, this situation is entirely without precedent. We have no prescribed etiquette to fall back upon. I shall continue to be flippant.


He does continue to be flippant. Soon, he says, “Certain women should be struck regularly, like gongs.” In context, it's a cheeky comment not meant to be taken seriously. To treat a woman like a gong is to suggest she’s meant to be struck. Because Elyot and Amanda fight, the playwright may be alluding to the way a gong is struck before wrestling matches in Japan. It could also be a reference to the way gongs call people to order. It’s equally possible that there is no deeper meaning to this quote beyond showing what a cad Elyot continues to be. As he says in act II, he won’t be controlled by the morals of others:


AMANDA: Don't laugh at me, I'm serious.ELYOT: You mustn't be serious, my dear one; it's just what they want.AMANDA: Who's they?
ELYOT: All the futile moralists who try to make life unbearable. Laugh at them. Be flippant. Laugh at everything, all their sacred shibboleths. Flippancy brings out the acid in their damned sweetness and light.


Elyot’s jest about “sacred shibboleths” is not entirely innocent, of course. He does hit his wife. Their relationship is abusive. There’s a lot of tragedy in this comedy.