What Really Matters is not What Someone Looks Like on the Outside, But What They are Like on the Inside.
Even if you don’t get the joke, the fact that this guy is even trying to pass himself off as someone else is amusing. In point of fact, we believe that this is the most significant problem that exists anywhere in the cosmos as a whole. But we cannot deny that he looks super cute.
Even his t-shirt, which features an image of x-rayed ribs, is a reference to a joke that only a select few people will understand. If the sign and costume are intended to be used inside, he can conceal both of them by pulling his shirt over his head and placing the hood of his jacket over it.