Act up (short video)

The phrase of the day is: "act up"

• if children act up, they behave badly
  [ --- The kids have been acting up again. --- ]
  
• if a thing acts up, it operates incorrectly
  [ --- My phone acted up again this morning. --- ]
  
• if a part of your body or a piece of equipment acts up, it starts to become painful or to develop problems
  [ --- I hope my back doesn’t start acting up again. --- ]