They mucked around in the office all morning without doing any real work.

mucked 是动词 muck 的过去式，muck 本意是"粪肥、污物"，引申为"弄脏、胡闹"。 muck around 是固定短语，意思是"无所事事地闲混、浪费时间"，通常指不认真工作或做事不正经。