act up
US /ækt ʌp/
UK /ækt ʌp/
1.
behave badly or improperly
:
•
The children started to act up during the long car ride.
•
If you act up again, you'll be sent to your room.
2.
(of a machine or part of the body) fail to function properly
:
•
My old car always starts to act up in cold weather.
•
My knee has been acting up ever since I went for that long run.