faire boutique mon cul

to earn your living through prostitution

Sex work described in the flat language of retail, where you keep a shop and the shop is your own backside. There is no euphemism anywhere in it. The phrase is West African argot, and it has followed the people who use it into French fiction as well.

Elle a fait boutique mon cul pendant des années avant d'ouvrir son petit commerce.

She worked as a prostitute for years before opening her little shop.

A compound of 'faire', 'boutique' and 'cul'. A version of it turns up in Alphonse Boudard's 'Madame... de Saint-Sulpice' in 1996, and Dominique Eudes later described the phrase as a definition straight from the oral trade register.