A: Your younger brother seems to have put on a lot of weight in the past year.

B: Indeed. The doctor has told him to do more exercise, but he won’t do it, he’s bone idle.

Note: This colloquial saying, mostly British, means “extremely idle or lazy.” The idiom dates back to the early 19th century, describing laziness that penetrates the very bones. Similar terms (bone lazy, bone sore, bone tired) predated it in the “Vocabulary of East Anglia” (1830). For nouns, we also say someone is a “lazy bone.”