Avram, respecting diversity includes respecting my right to object to a word, make fun of Jargon, etc.
NP, a custom against Chazal has no status. What if someone’s family custom were to drive to shul on Shabbat? In any case, as I wrote, there are other mitzvot involved and, IMHO, they push off some family chumra. If he wants to be a big machmir let him do a hattarat nedarim and then keep it b”n except in extenuating circumstances. Rav David (HaNazir) Cohen’s son Rav Shaar Yishuv did this regarding nezirut and then abandoned it at age sixteen.