It would kill the cat, not quickly though it would cause alot of pain and suffering and it would probably drag on for a while. I sincerely hope you aren't actually thinking of killing a cat anyway,...
Since cats (and dogs) metabolize drugs differently than humans this is not a great idea, if you are not a professional in animal care. You must take it to the vet as soon as possible to find what is...
Why would you want to use vicodin to kill a cat? Vets will euthanise a cat if it is clinically necessary. There are pet charities that could help you if you can't afford the fees. Euthanasia by vet...