I see no case here. However, this is a great way to get publicity for their Unicorn Latte.
Smart on the part of the Brooklyn cafe to trademark "Unicorn Latte" ...however people mislabeling it on social media is not the fault of Starbucks. Starbucks markets it as the Unicorn Frappucinno.
The drinks are entirely different. One is all jacked up on sugar and the other is in fact a health drink with raw cashews, pressed ginger, and lemon juice.
This cafe is either putting the case out there to get publicity or they're just a bunch of whiny babies (yest that's my opinion).