act up act up /ækt ʌp/

verb

1. Make itself felt as a recurring pain  ( act up )
   make itself felt as a recurring pain
    My arthritis is acting up again
   My arthritis is acting up again
   
2. Misbehave badly; act in a silly or improper way  ( act up , carry on )
   misbehave badly; act in a silly or improper way
    The children acted up when they were not bored
   The children acted up when they were not bored