Literal Translation
To backcomb each other’s bun (hair bun that is)
Actual Meaning
To have a row
Etymology
Etymologically, the word ‘chignon’ comes from the Latin catena (“chain”), which previously meant ‘nape of the neck’. Related to ‘chain’, ‘chaignon’ became ‘chignon’ in the 16th century, through a crossover with the word “tignon” (from ‘tignasse’) – or a mass of hair gathered at the nape of the neck. However, the meaning of the word ‘chignon’ as a hairstyle only appeared in the 18th century.
This expression marks a contrast between hair care and the violent acts that women can engage in when they fight each other. If ‘se crêper le chignon’ is used to refer to a dispute or a fight between women, it is because only women in the West can wear their hair pulled up and gathered behind or on top of their heads, forming a chignon.
So, the image behind this expression (which is somewhat misogynistic, as men also wear chignons) comes from the fact that when women fight, they can grab each other by the hair, completely destroying their chignons, which then look a mess.
As for backcombing, it consists of teasing the hair by pushing back part of each strand with a comb or brush. It could be that at the end of the fight, when the protagonists have their chignons undone and their hair all over the place, this could be attributed to an attempt at backcombing – an unsuccessful one at that.