As a noun, the Northern-English word mardy was first recorded and defined by ‘Leofric’ in Hallamshire¹ Vocabulary, in the column Local Notes and Queries of The Sheffield & Rotherham Independent (Yorkshire) of 3^rd August 1874:

Mard, adj.—Pettish, peevish, used in speaking of children. I hesitate to derive this word from “marred” in the sense of spoiled.
Mardy is the corresponding substantive, a spoiled child, and “To mard any one up” is to pet or caress with a foolish display of tenderness.

(¹ Hallamshire: the historical name for an area of South Yorkshire, in the current city of Sheffield)

As an adjective, mardy is first attested in this letter by the English clergyman and schoolmaster Ebenezer Cobham Brewer (1810-97), published in Notes and Queries (London) of 23^rd September 1882:

Mardy or Mawdy Child. A crosspatchy child in Nottinghamshire is called a “mardy child,” in the southern counties a “mawdy child.” I cannot find the word in any dictionary in my possession, including, of course, Halliwell. Is it the French maldit, a word occasionally met with in French books, but not admitted into French dictionaries?

In fact, although ‘Leofric’ hesitated “to derive this word from “marred” in the sense of spoiled”, mardy is probably from:
– mard, dialectal alteration of marred, meaning, of a child, spoilt,
– and the suffix -y, meaning having the qualities of, as in plumpy for example.

The past participle of mar, marred, has long been used to mean ‘impaired’ in character by excessive indulgence or leniency (this usage is comparable to that of spoilt, the past participle of spoil); for instance, in Of London (London, 1790), the Welsh naturalist, traveller, author and antiquarian Thomas Pennant (1726-98) wrote, about the Guildhall:

At the bottom of the room is a marble group, of good workmanship, (with London and Commerce whimpering like two marred children), executed soon after the year 1770, by Mr. Bacon.

In Shropshire² Word-Book (London, 1879), Georgina F. Jackson defined marred as meaning:

petted; foolishly indulged; spoilt.

(² Shropshire: a county of England, situated on the border with Wales)

It seems that there existed the rhyming phrase the mardy child is not a pleasant sight; on 1^st August 1911, the Sheffield Daily Telegraph (Yorkshire) reported that, during the debates at Leeds Assizes the previous day, the following exchange took place:

Counsel: Here is something you said about Mr. Roberts in 1906: “The mardy child is not a pleasant sight.” Ceasing to read the quotation, counsel interjected “I have never seen one. I don’t know what it means. What does ‘mardy’ mean?”
Mr. Derry: It is a local word. It means spoilt or squeamish.
Counsel: Well, now, are you not mardy?
Mr. Derry: No, I think I have been extremely patient on this occasion.
Counsel: Patience is a form of halo you have selected.
His Lordship: And his pedestal is the witness-box. (Laughter)
Counsel continuing the quote: “The mardy child is not a pleasant sight. I don’t think I ever before observed so thorough mardy a public man. How colossal must be the self-approbation of one who, when met with legitimate and inevitable public criticism, treats it all round as a personal affront.”

The Guardian (London) of 13^th October 1975 published English as she is spoke in Manchester, about Dr Peter Wright, who studied the speech sounds of this northern city:

The shops, the offices, the constant stream of visitors, mean that it [= Manchester speech] is more influenced, too, by standard English than in the surrounding areas. Not all the city sounds, though, would be instantly recognisable in the lobby of the Midland Hotel. Meithered³ mothers catching buzzes⁴ with mardy children are part of an earlier heritage.

(³ meithered: mithered – ⁴ buzzes: buses)

 

Lyrics of Mardy Bum, by Alex Turner (born 1986), from the album Whatever People Say I Am, That’s What I’m Not (2006), by the Arctic Monkeys, an English rock band formed in 2002 in High Green, a suburb of Sheffield, Yorkshire:

Now then Mardy Bum
I’ve seen your frown
And it’s like looking down the barrel of a gun
And it goes off
And out come all these words
Oh, there’s a very pleasant side to you
A side I much prefer

It’s one that laughs and jokes around
Remember cuddles in the kitchen
Yeah, to get things off the ground
And it was up, up and away
Oh, but it’s right hard to remember
That on a day like today when you’re all argumentative
And you’ve got the face on

Well now then Mardy Bum
Oh, I’m in trouble again, aren’t I?
I thought as much
Cause you turned over there
Pulling that silent disappointment face
The one that I can’t bear

Can’t we just laugh and joke around
Remember cuddles in the kitchen
Yeah, to get things off the ground
And it was up, up and away
Oh, but it’s right hard to remember
That on a day like today when you’re all argumentative
And you’ve got the face on

Yeah I’m sorry I was late
Well I missed the train
And then the traffic was a state
And I can’t be arsed to carry on in this debate
That reoccurs, oh when you say I don’t care
But of course I do, yeah I clearly do!

So laugh and joke around
Remember cuddles in the kitchen
Yeah, to get things off the ground
And it was up, up and away
Oh, but it’s right hard to remember
That on a day like today when you’re all argumentative
And you’ve got the face on