Definition: Stay out of trouble!
Example: Robby tried his best to keep his nose clean as he didn’t want to go back to prison. But the wedding cake in the bakery window was begging to be stolen.
There are a lot of claims as to the origin of this idiom…
1) It is a 1970s reference to cocaine usage, but the term predates this assertion by a century.
2) It is a childhood warning about personal hygiene and the spreading of germs through runny noses. There seems to be little supporting evidence for this.
3) It is a warning over the abuse of alcohol, that the foam from an upturned glass of beer ‘dirties’ the nose. Still not sold.
What we do know is that there was an earlier UK English phrase ‘keep your hands clean‘ which upon crossing the Atlantic to America, somehow morphed into keep your nose clean. It then returned to the UK and replaced the original phrase. Its meaning changed as well during its ocean crossing. The first version had more of a personal hygiene meaning, but in the States it took on more of a avoiding corruption twist. Most recently however, it seems to relate exclusively to the world of crime. Somebody keeping their nose clean is staying out of criminal activity.
Iddy’s had to borrow somebody else’s nose in order to illustrate the idiom. He doesn’t have one of his own.