(one's) ass is grass
1. rude slang One is going to get murdered. A: "We can't let that stool pigeon testify in court!" B: "Don't worry, boss, his ass is grass."
2. rude slang One is going to get beaten up. You say that to me one more time, and your ass is grass, Jim!
3. rude slang One is going to severely punished, especially by being fired, expelled, grounded, etc. A: "I heard Sarah got caught stealing from the cash registers." B: "Yeah, it looks like her ass is grass." Dude, if my parents find out I took the car without their permission, my ass is grass!