Saved by my own incompetence
I was once doing support for a CMS on the side.
Said CMS was never designed for large numbers of users and got seriously bogged down at one occasion. I found that the performance issues prompted many users to create multiple accounts (they never received a confirmation, but user records were still created), and that further slowed the system down.
So, I had the bright idea to clear out those half-broken accounts until things would easen up a little.
Opened up the SQL query tool on the server and prepared a DELETE command.
Sent the command off and then it dawned on me that I had forgotten the WHERE clause...
Imagine my relief when the query tool refused to execute the command because it was missing the semicolon at the end.