What does moi bubba mean in French?

"Moi bubba" is not a phrase in French. It's a combination of "moi" (meaning "me" in French) and "bubba", which is a Yiddish term of endearment, often used for a close friend or relative.

It's likely you heard this phrase in a context where someone was trying to be humorous or playful. It's not a standard French expression and would be considered unusual.