Now I thinking about it for a while and well maybe Beast boy isn't a vegetarian. I mean Beast boy is considered a vegetarian and even his voice actor is a vegetarian. But there is proof that proves against that.
1. In the Teen Titans go episode Bazaaro Titans (I think that's what the episode is called)
One of Robins of Robins in the book called The "Rules of Robin" is to eat heathy. Well Nibor (the opposite of Robin) tells them to eat meat and Beast boy joins in and also in that Laundry episode where Beast boy eats Hot dogs.
2. There is also evidence in the original teen Titans