(USA) If we stop to kick at every dog that barks at us we will never arrive at our destination in life, because we are obsessed with righting insignifigant wrongs that should have no more effect on us then a dog that barks as we walk by.
(UK) A large surplus of anything:
We've got enough coffee to cobble dogs with.
A cobblestone is a cut stone with a curved surface. These were set together to create road surfaces, in the days before the widespread use of asphalt. The image the phrase contains is that, even after all the roads have been cobbled, there are so many cobblestones left over that things that don’t need cobbling – such as dogs – could still be cobbled.
A cobbler repairs shoes, so if you have enough leather to cobble an animal with four feet or that doesn't need shoes, you have a surplus.
When you say that people fought like Kilkenny cats, you mean they fought valiantly to the bitter end, even if they are both destroyed. For instance, ''The two political parties fought like Kilkenny cats over the matter''
(UK) If someone is trying to convince people to do or feel something without any hope of succeeding, they're flogging a dead horse.
This is used when someone is trying to raise interest in an issue that no-one supports anymore; beating a dead horse will not make it do any more work.
A person who is generally known to have been guilty of some offence will always be suspected to be the author of all similar types of offence. Once someone has gained a bad reputation, it is very difficult to lose it.