mess around mess about
1. To tinker or fiddle with something. Hey, don't mess around with the thermostat—it needs to stay at 68 degrees. Grandpa's still messing around with that old radio, but I doubt he'll get it to work again.
2. To test or use something in order to learn more about it. I'm messing around with a different platform for my blog, and I can't decide if I like it or not.
3. To engage in aimless recreation or frivolous time-wasting; to fool around. Quit messing around and work on your book report already, Scotty!
4. To tease or play a prank on one, often by trying to get them to believe something that is not true. Come on, stop messing around. There's no such thing as ghosts.
5. To joke about something. Often used in the negative to indicate absolute seriousness. Oh, come on, Tina, we're just messing around. We didn't mean it. You guys, Mom is not messing around. She said she would ground us for a month if she caught us again.
6. To engage in casual sex acts with someone. Betsy and I are just messing around, which is great because I don't want a serious relationship anyway.