Starbucks doesn't even offer mermaid-themed drinks, which seems like an egregious oversight.
On the other hand, the finest coffee shop in all the land, The Black Cow Coffee Co in Croton, actually offers a drink called The Black Cow, which is like liquid heaven in a cardboard cup. They also have really tasty pastries and super-friendly folks working there. Go there. If you can't, tell your friends to go there. Actually, tell your friends even if you CAN go there.