Collins COBUILD Advanced Learner's English Dictionary - muck around

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