After seeing the zombie clown I would make a special infected based around that.
It would be similar to the witch (in size) except male, in an evil looking clown costume.
It would walk around slowly laughing insanely and if you get to close (like the witch), make too much noise (firing weapons when close) or even look (crosshair aimed on it) for too long it would attack.
It's attack would be similar to the Hunters except it when it pounces it incapacitates instantly and doesn't stay and attack, rather it runs towards another survivor to attack normally like a hunters/smokers normal swipe.
It would not be playable (like the witch) but would be much more common than her, as it would have very low HP to compensate for it's speed and strength.
Fun fact: I came up with that jut now with nio prior thought to it.