to behave in a silly way, especially in a way that might have dangerous results

Don't fool around with matches. 不要摆弄火柴。

to behave in a humorous way in order to make other people laugh

He's always getting into trouble for fooling around in class. 他老是因为在课堂上捣乱搞笑而惹麻烦。

to spend your time doing nothing useful

We spent the afternoon fooling around on the beach. 我们在海滩上闲荡了一个下午。

If a married person fools around, they have a sexual relationship with someone who is not their husband or wife.

She'd been fooling around with someone at work. 她和某个同事关系暧昧。