Left image: a well-built person wearing a tank top with the word "KILL" on an image of a skull.
Right image: a well-built person consuming whey protein from one of three flavours.
The image is funny because a well-built person wearing an aggressive tank-top with the word "KILL" on an image of a skull is having very childish flavours of whey protein such as teddy vanilla, yummy yummy choco, and strawberry vanilla, contrary to the person's external persona. This depicts the metaphor 'Do not judge a book by its cover'.