Ask HN: What's the most entertaining story of a technical mistake you've made?

We all make mistakes and sometimes looking back at those mistakes can provide a good laugh. I'm curious to hear stories others might have.

My favourite is from when I was in grad school and I connected two network interfaces from the same subnet onto a virtual bridge. This effectively meant my box was repeating all traffic on our lab's subnet. I was trying to debug my own network problems and was puzzled why I was getting duplicate ping replies. I left for class and figured I'd debug it later. Halfway to my class I finally clued into my mistake and rushed back to the lab. One of my labmates asked me if I was having Internet problems. I secretly reached under my desk to pull one of the two network cables and said no and we all got on with our day :)