to behave badly:
— My daughter always acts up at the supermarket when I refuse to buy her candy.
— If you don't stop acting up I'm going to send you down to the principal's office.
— I'm really sorry but your dogs will not be able to come to doggie daycare again if they continue to act up.
— Tell the babysitter to send me a text message if the kids act up.
— Have you noticed the children usually start acting up after drinking soda and eating candy? Perhaps you should limit their sugar intake.
to activate or start (especially describing illnesses or problems):
— The lawn mower was acting up today so I just asked our neighbor's son to cut the grass.
— My bad back is acting up again so I can’t play tennis today.
— My stomach has been acting up recently so I'd rather not eat anything spicy.
— My grandfather's arthritis acted up so he didn't come the beach with us.
— Has your internet been acting up today? Mine keeps cutting off and I've had to reset the router three times already today.
— My allergies are acting up. I can't stop coughing and sneezing so I made an appointment with the doctor to get an allergy shot.
More idioms will be added in the future so check back frequently or sign-up for my free newsletter to learn about new updates to my website.