#mdzs reference

let's start with Chinese Historical Customs: a married lady would have near total reliance on the backing and favor of her husband to have any power whatsoever within her household, or even be able to live comfortably -- without his backing and support, she'd be cut off from money, essential materials such as winter gear and heating fuel, even good food; the servants wouldn't bother listening to her (she'd have a few of her own brought from her first home, but not many); and being bullied (read: anything from humiliated to actually hurt) by her new family wouldn't be uncommon (and we all know what a pit of vipers the Jin Sect was even then).

doublespeak, face, and reputation, all meant that, intentionally or not, JZX was setting JYL up for a MISERABLE future life: by badmouthing her in public so everybody knows that her future husband thinks she's mediocre and unsatisfactory, he's saying he doesn't respect her (or her family! more on that in the next bullet point). if he doesn't respect her, he won't support her or help her if she needs him, because he doesn't care about her reputation, and therefore neither does he care about her comfort, or, well, about her... anything.

more Chinese Historical Customs, or, the Natal Family's Protection: a married lady's last backup defense is the fact that disrespecting her means disrespecting her family, who the husband has allied himself with by marrying her. the more they care about her, the more the natal family will respond to slights to her. they respond through retaliation -- by making the husband pay for disrespecting their daughter.

thus WWX's and JC's immediate answer of punching JZX for his remarks may have seemed disproportionate, but was actually not incorrect.

(They even gave JZX the chance to retract his words first!)

Stressors and Magnifiers: JZX isn't just being this dismissive in front of the two of them, which is already grounds for STRONG retaliation -- he's disrespecting their family's daughter right to their face!!! -- he's ALSO saying this to every single important peer they have, all of whom will go back home and tell that JZX, whose mother is dear friends with JYL's mother, and who visit each other all the time, and who thus must know her best... thinks she's so worthless, she can even be badmouthed in public. he's not only saying he will allow her to be disrespected by others, he's also drastically lowering her value to every other gentry prospect!!!

punching him was a brute and unrefined response, but it was a tradeoff: it traded away "face" for JYL's sake and protection. which she desperately needed right then. it sent the answer that disrespect towards JYL would be met by the strongest and most immediate retaliation the Jiang could possibly make;

and JFM agrees with the whole thing, because he finishes the move and breaks the engagement: "if you don't value her, then you don't get to have her".

(obligatory note that WWX was not expelled for his actions that day, and chose to return to Lotus Pier with JFM on his own... after finding out that LWJ had gone into seclusion and would no longer be around for him to tease.)

(obligatory note that it's extremely unlikely JZX was a malicious mastermind doing anything on purpose during this scene. we don't get a lot on him, but he was probably, honestly, just being a stupid teenager about a situation he was upset with. unfortunately, the above consequences still apply.)