Give (someone) an inch and (they'll) take a mile.

something that you say which means that if you allow someone to behave badly at all, they will start to behave very badly.

I'm always wary about making concessions to these people. Give them an inch and they'll take a mile.

• Don't sweat the small stuff.
• Don't take any wooden nickels.
• don't you dare
• do nut
• doom and gloom
• do one better
• do one better than
• do one better than someone
• do one better than something
• do-or-die
• door to door
• do own thing
• do part
• do proud
• dos and don'ts
• do share
• do someone any favours
• do someone a power of good
• do someone a world of good
• do someone dirt
• do someone proud
• do someone's bidding
• do someone's dirty work
• do someone's head in
• do someone the world of good