Means don’t drag up old drama, grudges, or awkward past events if it’s only going to kick off again. If everything’s calm right now, keep it calm. It’s basically the polite British superpower of avoiding unnecessary chaos. Honestly, half the country runs on tea and not reopening that group chat argument.
"Should we remind Dan about the karaoke incident at the Christmas do? Nah, let sleeping dogs lie. He’s finally stopped calling himself DJ Dynamo and we all deserve peace"