hair shirt 
noun
A shirt of haircloth, formerly worn by penitents and ascetics.She fasted savagely, stood barefoot on winter mornings while she recited all 150 psalms, and wore iron chains and a hair shirt till the day she died....
- It was not, he told me, a matter of wearing a one-size-fits-all hair shirt.
- For example, after the murder of Thomas Becket, Henry II went on a walkabout in a hair shirt to expiate his sin of accidentally-on-purpose suggesting that the cleric's removal would suit him right down to the ground.
adjective
(hair-shirt or hair-shirted) Austere and self-sacrificing: a hair-shirted existence advocated by eco-fundamentalists...
- The austerity is admirable but the effect of this hair-shirted self-punishment is too often not the revelation of a new affective range, but a dutiful boredom.
- Historically the product of a theocracy, Scots are imbued with the most hair-shirted of Protestant work ethics of hard work and reliability, with guilt, until recently a key driving force.
- ‘Ethical living’ was once the domain of hair-shirted hippies living in north Wales; now it has been adopted by the urban glitterati.