cool it
1. Calm down, relax, as in John was beginning to seethe, but I told him to cool it. [Slang; c. 1950]
2. Stop what one is doing, especially stop talking or behaving conspicuously, as in We'd be wise to cool it until the scandal blows over. It is also used as an imperative, as in Cool it! We'll be in trouble if anyone hears you. [Slang; c. 1950]