Working in Datacentres at a fairly young age, where the on-call rota often mean't I'd be rudely called in the early hours of the morning whilst slightly intoxicated in Fabric/Turnmills, it meant that strangely I made a number of mistakes.
Those that spring to mind involve accidently pressing the "Argon Release" button instead of the "Door Release", (why were they next to each other and the same god damn shape?). And once putting an SFP into a switch upside down, on a particular Cisco model that didn't prevent you from doing so, which shorted something and took down ~ 50 customers.