fool about

1. To play or tinker (with something), often in an aimless manner. Hey, don't fool about with the thermostat—it needs to stay at 68 degrees. Grandpa's still fooling about with that old radio, but I doubt he'll get it to work again. Why did I fool about with the settings on my computer? It's all messed up now!

2. To engage in aimless recreation or frivolous time-wasting. Quit fooling about with the dog and work on your book report already! If you three hadn't spent every lecture fooling about in the back, maybe you would have gotten a passing grade. Colin, stop fooling about with your friends and come inside for your dinner.

3. To joke about something. Often used in the negative to indicate absolute seriousness. Oh, come on, Tina, we're just fooling about. We didn't mean it. You guys, Mom is not fooling about. She said she would ground us for a month if she caught us again. Look, I'm not fooling about. Anyone who's late to my class again gets detention, end of story.

4. To have a casual sexual relationship with someone. Betsy and I are just fooling about, which is great because I don't want a serious relationship anyway. He caught me fooling about with my secretary, so our marriage is pretty much over. No, I don't want to just fool about. If you don't want to be in a committed relationship, then I think we should part ways.