mess about

verb

messed about; messing about; messes about

British, informal

1

: to spend time doing things that are not useful or serious : to waste time

We just messed about all afternoon.

She spent the evening messing about on the computer.

It's time we stopped messing about and got busy.

2

: to have sex with someone who is not one's husband, wife, or regular partner

His wife discovered that he was messing about (on her).

—often + with

Her husband discovered that she was messing about with her assistant.