don't tell tales out of school

Do not share secrets or spread rumors with other people, as doing so will likely cause problems for someone else and will alienate you from them. Hey, I heard what you were saying at the bar the other night. Here's a tip: Don't tell tales out of school about your co-workers, or you aren't likely to have any friends here before long. Hey, don't tell tales out of school. How would you like it if people broadcast your secrets, huh? Don't tell tales out of school, especially if you learned them by eavesdropping!