Don't you hate it when you have an itch you just can't cure? Sometimes it's physical, sometimes it's mental, sometimes the saying could probably be used as a metaphor for a problem in your life you can't get rid of, and possibly even need the assistance of someone else (just as long as you keep quiet about his wife and help him bury her). The point is, everybody has them. Except for those who don't.
I don't usually have my crocodile foot back scratcher on hand when I get a back itch, so I can commonly be seen rubbing my back against the town central tree (now the town central whore) like a grumpy old gorilla would.
Discuss all things back itches, and be free.