This term is one that is most indigenous to south Louisiana and New Orleans in particular. It is often used to refer to someone who is a low down scoundrel or to a woman with no sex appeal. However, though this can be a derogatory term, it is sometimes used as a complimentary term of endearment.
Derogatory: She's nothing but a coyoodle, and her husband is a low down coyoodle too.
Complimentary: It's good to see you, you old coyoodle you.