When I was teaching I was very lucky two have two wonderful classroom supports; one of them was a woman of a similar age to me who came, originally from Lincolnshire. She once remarked that a student had ‘a monk on’ and I was totally baffled. Thinking I had misheard her I didn’t ask, but when she used the phrase again I later wondered what it meant. It meant that the student was in a sulk, and it was the same as having or getting ‘the hump’ or having ‘the hump on’. My dad had a way of expressing it, he would say to me or my sister that we had ‘got one on us’.
The camel phrase dates from the seventeenth century, ‘monk on’ may come from naval slang, or it maybe a derivation from rhyming slang, monk/chipmunk/chip on your shoulder. This sounds imaginative to say the least! It is certainly a phrase which has been used in Cumbria, Yorkshire and the East Midlands. Maybe it as obvious as a person in a bad mood not talking, and monks being sometimes in a silent order.
This evening, I used my dad’s phrase, and my husband, brought up in Cornwall and Surrey and living for thirty years in Lancashire, had no idea what I was talking about!
Lois Elsden 
I was born in Yorkshire (Sheffield) and one would say something like….”she’s got Monk on today….”. I think the meaning varied according to the context.
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Just to be absolutely accurate, we would not say “got a monk on” but we would drop the “a”….i.e. he’s got Monk on…”
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We lived on the border with Yorkshire.. you’re right, ‘a’ was often dropped… I’d forgotten!
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Here in Canada when someone is in a bad mood we often say Who pooped on your Corn Flakes?
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LOL… it’s the sort of thing my husband would say!!!
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