Why my cat stinks and my cousin's cat smells vanilla & cookies :/?

I don't know about vanilla or chocolate, but you may consider changing his food. He could also have bad teeth. Cats get plaque and abscesses just like we do. Have a vet check him out to be sure he is healthy. Then, stop feeding him seafood. It makes his breath stink and his hair, when he washes. I use chicken/turkey/beef flavored food: No stinky breath! Then, no stinky hair. My cat likes Fancy Feast and Friskies Indoor.