What's the biggest issue you have seen where an admin changed something and caused a business disruption?

Several employers ago, and not really NetSuite that caused this issue, but someone (not me!) edited a product in NetSuite during Black Friday. These changes hit the website which because of a design flaw and peak traffic cause a caching cascade that brought down the whole website for about an hour. On Black Friday. ~100k in lost sales.

Enabling Advanced Bin Management without consulting developers about script impacts.