when the cat's away

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."
See also: mice, play, will
Farlex Dictionary of Idioms.

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.
See also: mice, play, will
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

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.
See also: mice, play, will
The American Heritage® Dictionary of Idioms by Christine Ammer.

when the cat's away

or

while the cat's away

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.'
See also: away
Collins COBUILD Idioms Dictionary, 3rd ed.

when the cat's away, the mice will play

people will naturally take advantage of the absence of someone in authority to do as they like. proverb
See also: mice, play, will
Farlex Partner Idioms Dictionary
See also:
  • when the cat's away the mice will play
  • when the cat's away, the mice will play
  • walk all over
  • walk all over (someone)
  • walk all over somebody
  • lose (one's) hold over (someone or something)
  • responsible party
  • take charge
  • prophet
  • a prophet is not without honor save in his own country
References in periodicals archive
"When the Cat's Away" (Sony), set in a run-down Parisian district in the process of change, has more style and originality, and gives us a convincingly rueful look at a lonely young woman gradually coming to terms with the life around her.
A small movie, "When the Cat's Away" begins when Chloe (Garance Clavel), about to go away on vacation, has to find someone to take care of her cat, Gris-Gris.
When the Cat's Away