A function that consisted of a giant switch statement, with each case consisting of another switch statement. Half of the sub-cases contained GOTO statements back to the top of the function.

Even worse... I wrote the code. It was 2am, I had been working for 18 hours straight to get everything ready for a demo the next morning.

Even worse than that... the code worked so management wouldn't let me change it. I tried my best to find an edge case it wouldn't handle but never could. So the code shipped.