I think I can make an interesting point on this, having inadvertantly set off a foaftale many years ago. Sadly, it was highly localised, but taken as a sample, it could shed some insight.
Anyway, I was working in an MOD establishment (NOT as a secret agent, as one decidedly paranoid UFO author came to believe, but as a mere wages clerk) and the office discussion of the day somehow got round to lesbians. Please note that there were women in the group too, so the fellas could not really work in the topic of what they had seen in certain films; the commentary, in fact, had to be fairly tame in tone.
Before I continue, a disclaimer: I was only seventeen - what else would you expect me to say?
Some young lady piped up about the fact that lesbians cannot have penetrative sex. A truism, I thought - until inspiration hit me:
"Depends if you got a cucumber handy, though, dunnit?"
As I said - I was only seventeen.
The girl who raised the point turned away in disgust. The chaps mused abstracedly for a moment, then went back to work. And then one particularly strange lady - let's call her Clarissa, just in case - fled the office, crying.
Seriously. She was that strange. She had reputation for it. The office leading hand informed me that she was very sensitive, and I should not have made the remark about cucumbers. Not in front of her, anyway.
Six months or so pass...
Coming back into work after a liquid lunchtime (I was eighteen by then, so it was allowed) meself and some of my office mates were accosted by one of the dockies (as opposed to dockers, who only work in civilian yards) from the other end of the establishment (and it was a big establishment, too - a good several miles square, at least) who raised the subject of Clarissa. "What happened with her and the cucumber sandwiches, then?" he asked? Clearly, he meant my remark - which we'd all pretty much forgotten about by then - and we explained the situation to him. How the story had ended up being about 'Clarissa and the cucumber sandwiches' as opposed to 'Clarissa and what somebody said about a cucumber' is anyone's guess. But it does leave me wondering if the Chinese Whisper explanation - that a relatively ordinary story can auto-confabulate into something more foaf-ish - has something going for it.
Alas, being three sheets to the wind at the time, I cannot recall the particulars of the 'cucumber sandwiches' story itself.