Givesomeone an inch and he'll take a yard.

Give someone an inch and he'll take a mile. & Givesomeone an inch and he'll take a yard.

Prov. Be generous to someone and the person will demand even more. (Describes someone who will take advantage of you if you are even a little kind to him or her.) •

If you let Mark borrow your tools for this weekend, he'll wind up keeping them for years. Give him an inch and he'll take a mile.