I'm not bossy, I just know what you should be doing. (thanks to Eggs Benedict)

How to poison animals (any kind of animal)

Disclaimer: I neither support nor endorse unethical poisoning of animals that cause no trouble.

To kill a cat: give it a tablet of acetaminophen (tylenol, paracetamol)
To kill a dog: share with it your milk chocolate of choice
To kill a parrot: let it sip coffee. Alternatively, chocolate can also do the job.
To kill a hamster: almonds. They'll love their last supper.
To kill a horse: too many to list. see http://www.extension.org/faq/15
To kill a rabbit: soy beans, orange peels and/or onions.
To kill a turtle: include cauliflower in its diet.
To kill rats: DDT
To kill pet cockroaches: sorry, you can't kill cockroaches