A person who is noted for being mardy
– that is to say demonstratively miserable. Being depressed doesn't count – the mardy arse revels in unhappiness and broadcasts it via sulking, moaning, whingeing
and (in the case of children) crying at the drop of a hat. An element of paranoia will generally be present; the mardy arse permanently feels hard done-to.
Perhaps the key difference between grumpy and mardy is that the former involves more anger and the latter more self-pity. However, in an almost bipolar way, the mardy arse will tend to be someone who mood-swings from mardy to lary
– from surly/resentful to surly/aggressive – often when alcohol has been added as a catalyst.
The term is a coarser and therefore more emphatic version of mardy bum
(the 'bum' in this sense referring to the buttocks, not a beggar or hobo, and 'arse' being a less polite word than 'bum'). It may be heard in the same Derbyshire, South Yorkshire, Nottinghamshire, Leicestershire zone of the English East Midlands where mardy is commonplace, though principally the city of Leicester.