That's probably a prime example of differences in perception: to me, the intended effect (and the fact that it's Photoshopped) was immediately obvious. And I kinda wondered why her upper mouths have been edited to remove some of the teeth... She does look creepy, for a moment, which is part of the reason it looks funny.
There are several other versions out there, possibly
not copies of each other; the concept itself isn't all that difficult to come by, once you realize the implications of the fact that eyes represent emotions at least as much as mouth.
<-- One could black out the mouth and it'd still be clear it's a happy emoticon.
