Last night I had two kegs of carbed Hefeweizen that I wanted to take to a party. One had 1 gallon in it, the other 2 gallons.
Thinking I didn't care about sediment (being a Hefe and all), and being a little druck, and being too lazy to set up my usual keg transfer QDs, I just opened each corny up, and poured the little into the big. I was quickly treated to the sight of foam climbing up the keg, and flowing non-stop out the top.
The tower of foam would have been a beautiful sight if it hadn't been caused by my own stupidity. And I ended up with less than the original 2 gallons in the keg.
Feel free to share your own moments of stupidity.