mother-in-law style

Wiktionary

1. n. linguistics, anthropology The style of speech and manners which are to be observed between an Australian aboriginal man and his mother-in-law (i.e. wife's mother). Depending on the particular people this can go so as far as an entirely separate vocabulary of words. (Reference: Macquarie Aboriginal Words, Macquarie University, 1994, paperback ISBN 0-949757-79-9, introduction.)