OK, this isn't just limited to design stuff, but...
During the course of designing various aircraft, it has been my fortune (and, sometimes, misfortune) to have had to hand numerous design standards. For us Human Factors bods out there, our bibles include MIL-STD-1472, Def Stan 00-25 and, of course, the veritable Def Stan 00-970.
The big difference between US miltary standards (MIL-STD's - available through http://assist.daps.dla.mil/online/start/ , but you need to register/apply) and the UK Defence Standards (Def Stan's - go to http://www.dstan.mod.uk/ ) is that the US military thinks further ahead... Once the design is complete, then it has to be tested. Therefore, the standards include not only specifications for stuff, but also test methods and the correct way of reporting test failures.
From time to time, one comes across standards that seem to have kept someone more busy writing them than those actually building the relevant equipment. My favourite comes from the States: the "must have" for every designer's pocket... MIL-B-44229 - Beef and Carrots In Gravy, thermostabilised, tray pack (now, apparently, cancelled). It not only has the full specification for the beef, the carrots AND the gravy (and all constituent parts, as well as foreign objects), it also has the procedure for reporting any failures. For example, "Major Failure Code 06: Carrots are hard or tough", or, "Code 12: Gravy is lumpy."
I understand that there is also a Def Stan for "Mars Bars", dating back to the Falklands War, but I've never seen it, so I can't verify if that is true. A search of current standards provides no info on current UK military chocolate bar standards.
So, the question: what is the silliest standard you've ever been asked to design something to, or to work to (both civil and military standards)?