British, humorous the way in which plans fail and bad things happen where there is any possibility of them doing so.
It's Sod's Law that on the one occasion when the train arrives on time, I'm late!
sod's law
noun a cynical 'law' of existence that decrees that 'if something can go wrong it will' and is therefore named or cited as explanation or justification whenever such circumstances conspire UK, 1970