A Russian equivalent to “give them an inch and they’ll take a mile” is посади́ свинью́ за стол – она́ и но́ги на сто́л. It means “seat the pig at the table – she’ll put her legs on the table”

I'm no fan of Winston Churchill quotes, but I have to give it to him, his pig soundbite was pretty decent… “I like pigs. Dogs look up to us. Cats look down on us. Pigs treat us as equals.”