I once had a correspondence game online like this, where I blundered like that... and it's not even like I moved quickly, I had actually taken 10 minutes with the position... but completely missed an obvious threat.
It really should never happen... there's no excuse when you have all the time you want, but sometimes it happens.
Ever outplay your opponent from move 1, and pick the very worst time to blunder? Forced mate in 13 by the way.