I accidentally started a reindex on a collection that had 14 million records in the middle of the day. Caused an outage in a major portion of our applications for about 3 hours. Worst thing was that once I pressed enter, I realized that it was for the production database, and not the staging database like I intended. I immediately went to go tell the dev ops lead, and he basically said, "whelp, let's just sit back and watch the world burn. Not much we can do about it"