“The best hangover cure I know is some hair of the dog that bit you. A little more alcohol the next day will make you feel better!”
Question: Is it a joke or does it really work? Is this phrase only used in this situation of hangover?
Thank you.
I’ve never heard it before, but I quite like it 
It’s mostly an urban myth, IMO. The expression is interesting, it seems to come from the superstitious idea that you need to use the hair of a dog in order to cure the injury that its bite caused you. It’s an example of so-called “sympathetic” magic.
Nowadays, it seems to be used either in the case of hangover cures or as an expression in economics.
Economists from liberal schools (such as the Vienna school) criticize the proposal of Keynesian economists that you should increase public expenditure in order to activate economy by pointing out that it is a “dog hair” proposal: they think that excessive expenditure causes recessions and spending even more will only exacerbate the issue.
There’s a couple of very funny videos on youtube where the controversy between Hayek and Keynes is presented as a rap battle. They use several terms that include “hair of the dog”. This is the first of the videos:
The “hair of the dog” bit shows up around this time: