Richard, this is absolutely fascinating. I grew up on a flattish, clay course half an hour south of London where there was no quirk, at least nothing I regarded as such. I think I got my first taste at St. Enodoc which my dad and I played often on holiday. The rumpled fairway at the 1st was unlike anything I had seen before (instantly fell in love with it), but I didn't really regard it as quirky because I'd read that sort of thing was common/usual/standard on links courses. The approach between the dunes at the 2nd was, again, weird and fun to me but not really quirky. The 3rd, likewise, was very different and perhaps my favorite hole for many years (since overtaken by the 16th) but not really quirky. The 6th with the Himalaya Bunker was obviously very strange, beautiful, amazing, weird and yes quirky to me, but I think from a young age the first hole I regarded as quirky was the 4th...but I didn't know why.
Have you played St. Enodoc? And does any of this make sense, or do I have to think some more on what quirk actually is?
You think there is a clear definition, but might it also be in the eye of the beholder? Also, where on a golf course does quirk happen most often?