If someone has a hair of the dog, they have an alcoholic drink as a way of getting rid of a hangover, the unpleasant effects of having drunk too much alcohol the night before. It is commonly used as a way of excusing having a drink early on in the day.
A hangdog expression is one where the person's showing their emotions very clearly, maybe a little too clearly for your liking. It's that mixture of misery and self-pity that is similar to a dog when it's trying to get something it wants but daren't take without permission.
If you wish to be associated with a particular high risk and/or high profile situation and benefit from the rewards of that association, you have to accept the consequences if things go wrong - you cannot dissociate yourself.
Said of a salient point in a television show or other activity at which the popularity thereof begins to wane: The Flintstones jumped the shark when a man from outer space came to visit them. The expression derives from an episode of the television sitcom 'Happy Days' in which Fonzie, clad in leather jacket and on water skis, jumps over a shark. That episode was widely seen as the beginning of the end for the formerly popular series.