Writing a backend (horrific mainframe stuff) to a web form. The fact that it submits XML to us which is converted to a flat file and transferred onto a hideous DBMS via a suite of COBOL batch apps isn't even nearly the worst part.
Business side: "We don't need any validation."
They went on to explain, with around 25 pages of lists, the validation required.
Me: "Er, I thought you didn't require any validation!"
Business side: "We don't! Now, if the procedure code is '7600' you need to make sure that..."
My last day here is next Friday.