I assume this is a cultural thing that I am not aware of, but a friend just updated their status to say:
Xīwàng māo jiù biàn chéng tiānshǐ shǒuhù quán jiā
Who or what is 猫舅?
I don't know the word "猫舅".
舅舅 is used to refers to a brother of your mother. If one's mother is A, and she has two brothers: B and C,
So I guess 猫舅 is used to call a brother of the cat's mother. In your example, you friend uses this word from a cat's view.
My guess is:
Your friend might have some dogs, cats and other animals as pets. He might want to regard all these pets as a big family, to each member of which he might want to give a lovely nickname. For example, he might have:
猫舅 in this sentence just means cat. It's become slang to say 猫舅 when one just means cat.
Also the following might be helpful too: