Anyone ever come across this one? It's not very dirty or witty, but it's the very first limerick I heard when I was about 4 which is 56 years ago. The old lady next door told me it and she was from King's Lynn but living in Hull.

There was a young lady from Spain
She cocked her leg over a train,
The train went fast
And tickled her arse
There was a young lady from Spain

I seem to remember there were lots of children's limericks around then that repeated the first line at the end.