The "Ballygawley roundabout beacon".
A P3 navigator, new to NI, was forever confused when asked to dial it up (on a totally spurious frequency, of course, as it didn't actually exist). Oh, how frustrating for him as he could
never get the needle to lock on. We used many varied excuses (Oh, sorry, I forgot, it's NOTAMed u/s today, Tom. We're probably flying just a bit too low to get it this time, Tom. It's a bit of a dead area, here, Tom. Never mind. Try again on the way back, Tom).
Obviously, when one of the two winged master race dialled it up, it always worked immediately and the needle swung straight to it as we passed by, no matter what.
By setting the box to "test", of course.
I left the province wondering if he ever realised it was a total setup, for his personal benefit.
Talking of spoofs, what about the impossible to find co-pilot, "Albert Thirlkettle"?