Translation:My drunk parrot is not the worst, Marcus!
It's the vocative case. I think it's rarely used.
"The vocative case ... is usually the same as the nominative, as in English, and it is used when you address someone directly. The exceptions to the rule that the vocative is the same as the nominative are summarized in the phrase, Marce mi fili, which is the vocative for Marcus meus filius, and is a convenient way to remember that all 2nd declension nouns in -us, have a vocative in -e, that the vocative of meus is mi, and that all 2nd declension nouns in -ius have a vocative in -i."
In most declensions, the vocative is exactly the same as the nominative. As I recall, it's only in the case of second declension singular nouns that the cases are differentiated. So, 'Psittacus ebrius meus non est pessimus, Livilla!' would be correct, or 'Psittacus ebrius meus non est pessimus, pater!', but not 'Psittacus ebrius meus non est pessimus, Marcus!'
I'm getting very tired of questions about drunk parrots. It was very slightly amusing to begin with and demonstrated an interesting usage of two words. But I believe this constant repetition means an opportunity to teach more useful phrases is being lost through programming that is either lazy or misguided.