When I was in college and working on campus as a web developer I did a find-replace. I was in a hurry to get to my next class so I committed it in SVN and ran t

When I was in college and working on campus as a web developer I did a find-replace. I was in a hurry to get to my next class so I committed it in SVN and ran to class and muted my phone. When I went back to work a couple hours later I learned that my quick find-replace had taken down the entire campus email system. Apparently, I had broken something which caused automated error emails to be sent. However, I also learned that I had broken the method that sends the emails so it triggered a new error after sending the email and then tried to resend the original email. After a short period it had overloaded the campus email server. Thankfully, my boss was understanding but we had a nice long talk about testing code before committing it and not relying on automated tools like find-replace. There was also a new policy created about doing code reviews shortly after.