three-scallop problem
A problem whose solution is very obvious to everyone else, but which for some reason they refuse to divulge to someone who needs to find these things out. From the movie Demolition Man, starring Wesley Snipes and Sylvester Stallone, where in a future world of perfect primness no-one has the nerve to explain to Stallone's defrosted cop the purpose of the three seashell-shaped markings in every toilet.
They're not telling me what's up with Diane these days. It must be a three-scallop problem.