A British police euphemism meaning to keep out of trouble, commit no crimes
Stay out of trouble and do as you're told.
It is not an idiom, it means your nose is itching.
From horse racing, where they judge the winner of the race by which horse's nose crosses the line first.
An idiom is a phrase that makes no sense unless you know the definition. Can a nose actually run somewhere? No, so this is an idiom.
This idiom comes from horse racing. You'd bet on whichever horse's nose would come in first. If you make a good guess, you're "on the nose."
say no to it
To poke your nose into is to insert yourself into someone else's business.
Use a nice, clean, damp sponge to clean the inside of the horses nose.
The tiny hairs in our nose clean the dust particles in the air
If the piercing is recent, very carefully, once it is healed, you can clean it as usual.
It's not an idiom, it's a description. It's when you bleed from your nose.
The most common phrase is "nose to the grindstone," as in "He really has his nose to the grindstone this week."