Muck about / around / up

To muck about or muck around is a British colloquial expression that means to act or behave in a pointless, unproductive way, and dates from the late 19th century. To muck something up means to spoil or make a mess of something. All these meanings derive from 'muck', which is a very old word of Norse origin that dates from before the 12th century, which means farming manure, or any dirt or mess in general.