My personal story is Mists of Pandaria pre-patch. I made a change to fix a boat problem with CRZ the day before, and it made a bad assumption that chain crashed when pushed to the live environment. I remember making a fix for it and asking my lead how to verify in QA...

"Well, Kurtis, you need live to verify, and you can't make things any worse...." I felt really bad, but in hindsight it's pretty funny. Like - you can't break what's already broken, dumbass. :-)