mess around

informal
to spend time doing various things that are not important, without any particular purpose or plan:
They spend their weekends messing around on their boat.
My brother likes messing around with computers.
He spent the day with friends, just messing about.
He spends all day messing around with the dogs instead of working.
Stop messing around watching the telly, and come and help me.
We spent the week messing around in the cottage.
I need to stop messing around and make some decisions.

to behave in a stupid or annoying way:
Stop messing around and listen to me!
(Cambridge Advanced Learner's Dictionary & Thesaurus からの mess around の定義 © Cambridge University Press)

アメリカ英語辞典
to waste time doing something without a particular purpose:
The kids were just messing around at the mall.
(Cambridge Academic Content Dictionary からの mess around の定義 © Cambridge University Press)

- Cambridge Dictionary