act up

British  

verb

1. informal (intr, adverb) to behave in a troublesome way

   the engine began to act up when we were miles from anywhere

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act up Idioms  

1. Misbehave. For example, With an inexperienced rider, this horse always acts up . [c. 1900]

2. Malfunction, as in I'm not sure what's wrong with my car, but the transmission is acting up . In both usages up means “abnormally.”

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Example Sentences

In her four-star review Midgley suggested the show occasionally "feels scripted", noting the Furys know that "the cameras are on them and perhaps act up for them".

From BBC • Aug. 18, 2023

“You ain’t stoppin’ what’s goin’ on with me sweetheart,” Palmer lip-synced.“So if you gon’ act up, I’m ’bouta link up, I’m ’bouta link up, I’m ’bouta link up.”

From Los Angeles Times • Aug. 16, 2023

First, people who dress up don’t act up.

From Seattle Times • Jun. 19, 2023

Lopez says she hopes to keep playing for many years, even if her knee is starting to act up a bit.

From Reuters • Aug. 5, 2022

Wes didn’t act up in class, which kept him under the radar; his teachers spent 90 percent of their time dealing with the 5 percent of kids who did.

From "The Other Wes Moore: One Name, Two Fates" by Wes Moore