1.
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 BRIT INFORMAL )
We do not want people of his age mucking around risking people’s lives...
He’d spent his boyhood summers mucking about in boats...
= mess about
PHRASAL VERB : V P , V P prep / adv
2.
If you muck around with or muck about with something, you alter it, often making it worse than it was. ( mainly BRIT INFORMAL )
The president’s wife doesn’t muck around with policy or sit in on Cabinet meetings.
= mess around
PHRASAL VERB : V P with n
3.
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 BRIT INFORMAL )
He does not tolerate anyone who mucks him about.
= mess about
PHRASAL VERB : V n P