Definitionsregional note: in BRIT, also use muck about
1. phrasal verb
If you muck around or muck about, you behave in a childish or silly way, often so that you waste your time and fail to achieve anything. [mainly British, informal]
[V P] ⇒ We do not want people of his age mucking around risking people's lives.
[V P prep/adv] ⇒ He'd spent his boyhood summers mucking about in boats.
[V P prep/adv] ⇒ The last I saw of him though he was mucking about with the nurses and really enjoying
2. phrasal verb
If you muck around with or muck about with something, you alter it, often making it worse than it was. [mainly British, informal]
[V P + with] ⇒ The president's wife doesn't muck around with policy or sit in on Cabinet meetings.
3. phrasal verb → muck If you muck someone around or muck them about, you treat them badly, for example by not being honest with them or by continually changing plans which affect them. [mainly British, informal]
[V n P] ⇒ He does not tolerate anyone who mucks him about.
COBUILD Advanced English Dictionary. Copyright © HarperCollins Publishers