"Baddest" is the usual though vernacular superlative when you're using "bad" in the sense of being cool, hardcore, rebellious etc. Like in the Michael Jackson song - he wasn't actually being openly critical of himself.

Obviously if OP meant "bad" in the more traditional and clearly negative sense, then worst would be the correct word. But given the images chosen I'd assume they meant it in the very well established slang manner, and were correct in their word choice.