give somebody an inch

US /ɡɪv ˈsʌm.bɑː.di ən ɪntʃ/
UK /ɡɪv ˈsʌm.bɑː.di ən ɪntʃ/
"give somebody an inch" picture
1.

donner un pouce et prendre un kilomètre, abuser d'une petite concession

to allow someone a small amount of freedom or advantage, which they then try to exploit to gain much more

:
If you give him an inch, he'll take a mile, so be firm with your boundaries.
Si vous lui donnez un pouce, il prendra un kilomètre, alors soyez ferme avec vos limites.
My boss is very strict because he knows if he gives us an inch, we'll slack off.
Mon patron est très strict car il sait que si il nous donne un pouce, nous nous relâcherons.