to behave in a silly way

Stop playing around and get on with your homework! 别瞎闹了，抓紧做你的家庭作业吧！

I wish you wouldn't play about with that - you'll break it. 我希望你不要瞎弄那个东西了——你会把它弄坏的。

If someone who is married or has a serious relationship plays around, they have sex with another person or people.

If she finds out he's been playing around with his secretary, there'll be trouble. 如果她发现他一直在和秘书乱搞的话，那就麻烦了。