Give an inch and take a mileが妥当でしょう。一インチだけ譲ったのに一マイルもとるなんて。give an inch and they'll take a mile, Give someone an inch and he'll take a mile.のように使われます。I give you an inch and you take a mile!0:22
http://www.youtube.com/watch?v=j7H2qWZSAYs 0:47 he's not doing an inch, so don't give him a mile. あなたの息子さんは簡単なことも出来ないのに、もっと仕事を押し付けるのは無理ですよ。
https://www.youtube.com/watch?v=cJl6e2ggpu0 10:01 you give her an inch, she takes a yard like crabgrass.
参考リンク
https://bridge-english.blogspot.com/2020/05/the-camels-nose.html The Camel's Nose ラクダの鼻
練習問題解答
a-6361 don't give him an inch
b-0736 if you give him an inch, he will take a mile.
