when the cat's away, the mice will play

When someone in authority is not present, those subordinate to that authority do whatever they want. A: "If I leave my classroom for even a moment, I come back to find the place in chaos." B: "When the cat's away, the mice will play."

Prov. When no one in authority is present, the subordinates can do as they please. When the teacher left for a few minutes, the children nearly wrecked the classroom. When the cat's away, the mice will play. Jill: You shouldn't be reading a novel at your desk. Jane: But the boss isn't here. And when the cat's away, the mice will play.

Without supervision, people will do as they please, especially in disregarding or breaking rules. For example, As soon as their parents left, the children invited all their friends over-when the cat's away, you know . This expression has been a proverb since about 1600 and is so well known it is often shortened, as in the example.

If you say when the cat's away or while the cat's away, you mean that people behave badly when their boss or another person in authority is not there. While the cat's away — while a supervisor was out, employees were coming in late. When the cat's away... While Mr Schroder was on his travels his rivals were winning points at home. Note: People sometimes say the whole phrase, when the cat's away, the mice will play or while the cat's away, the mice will play. `You seem to be having a good time!' — `While the cat's away the mice will play.'

When the authorities are absent, people will break rules and do as they please. This proverb, which exists in numerous languages, appeared in several different forms in English in the seventeenth century. Thomas Heywood used it in A Woman Kill’d with Kindness (1607): “There’s an old proverb—when the cat’s away, the mouse may play.” Today it is often shortened.