Błędnie: The elderly lady regarded Mary's behaviour as an intact which she will definitely remember till the end of her days. Poprawnie: The elderly lady regarded Mary's behaviour as a faux pas which she will definitely remember till the end of her days.
"Nietakt", "gafa" to 'faux pas', 'gaffe'. "Popełnić nietakt" to 'commit a faux pas/gaffe' lub, bardziej potocznie, 'make a slip', 'goof'. 'Intact' to przymiotnik oznaczający "nienaruszony", "nietknięty"; "dziewiczy", "bez skazy".