What do you mean you bought resurrection armor for the dog?

It means you did something unusual or took a big risk. The expression "bought a resurrection nail for the dog" is usually a joke or a mockery, which means that you have done something unusual or taken a great risk. In the game League of Legends, "Resurrection armor" is a kind of equipment that can make players resurrect immediately after death. So the sentence "bought a resurrection nail for the dog" can be understood as "I did a stupid and childish thing, just like buying a resurrection nail for the dog". In a word, this sentence is usually used to express a humorous or joking tone, rather than to truly describe a fact.