to use or treat something in a careless or harmful way

I don't want him coming in here and messing around with our computers. 我不想让他到这儿来摆弄我们的电脑。

Never mess around with scissors. 绝不能玩剪刀。

If a married man or woman messes around with someone, they have a sexual relationship with someone who is not their wife or husband.

She found out that her husband was messing around with his secretary. 她发现丈夫和他的秘书偷情。