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.
This is an expression meaning that if you are going to get into trouble for doing something, then you ought to stop worrying and should try to get everything you can before you get caught.
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.
Usually refering to a small dog attacking a larger animal, this means that fierceness is not necessarily a matter of physical size, but rather mental/psychological attitude.
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.
This idiom means that people cannot change basic aspects of their character, especially negative ones.
("A leopard doesn't change its spots" is also used.)
Once a whale is on a beach, it cannot get back into the easily, so if you are completely stuck somewhere and can't get away, you are stranded like a beached whale.