A chap I know was having a quiet drink with some friends in a club on Pall Mall. A lady of about eighty strode up to them. She appeared to be no stranger in the land of gin.
'I just spazzed a monkey on the gee-gees,' she exclaimed, and then looked at them all sternly. 'Now, do any of you young men know what that means?'
She was terribly impressed that they all knew that she had lost £500 betting on race horses, and wandered off without further conversation. I'm more impressed with her. I like the idea of a lady who goes around springing surprise tests of slang on the youth of Britain.
And, in case you were wondering, a pony is £25, and a Dead Brazilian = Ayrton Senna = Tenner = £10.
As for quid, nobody is sure. It may come from quidditas in Latin, meaning that which is, perhaps with the sense of hard cash against airy nothings. But it may come from cud, as in the thing that cows chew. The idea is that cud came to refer to chewing tobacco and therefore to the little piece of tobacco to be chewed. It then came to mean any small amount of anything, and hence a unit of money.
Anyway, the first use of quid comes from the 1661 classic Strange News From Bartholomew Fair:
The fool lost his purse, but how he knew not; for the reckoning being suddainly brought in, his Quids were vanisht.
The Horologicon is a book of the strangest and most beautiful words in the English language arranged by the hour of the day when you will really need them. Words for breakfast, for commuting, for working, for dining, for drinking and for getting lost on the way home. It runs from uhtceare (sadness before dawn) to curtain lecture (a telling off given by your spouse in bed). It's out all over the world and you can buy it from these lovely people: