STAB IN THE BACK

(1) {v. phr.}, {slang} To say or do something unfair that harms (a friend or someone who trusts you). * /Owen stabbed his friend Max in the back by telling lies about him./ (2) {n. phr.}, {slang} An act or a lie that hurts a friend or trusting person; a promise not kept, especially to a friend. * /John stabbed his own friend in the back by stealing from his store./ * /My friend stabbed me in the back by telling the teacher I was playing hooky when I was home sick./