Meaning: To waste time:
* "Stop messing about and get your homework done!"
* "We spent the whole afternoon messing about in the park."
* "Don't mess about with your future, it's important to be serious."
Meaning: To behave playfully or foolishly:
* "The kids were messing about in the water, splashing each other."
* "He's always messing about, never taking anything seriously."
* "They were messing about with the computer, trying to hack into it."
Meaning: To fiddle or tinker with something:
* "He was messing about with the car engine, trying to fix it."
* "Don't mess about with that electrical wire, it's dangerous."
* "She spent hours messing about with her makeup."
Meaning: To treat something carelessly or disrespectfully:
* "Stop messing about with my things!"
* "Don't mess about with the furniture, it's antique."
* "He was messing about with the company's finances, and now he's in trouble."
Note: "Mess about" is a colloquial expression that is generally considered informal. It's more common in British English than American English.