Bad teeth, a lazy eye, or 80s mall hair/mullet?
As much as nasty teeth turn me off, let’s face it, there’s no getting around a freaky eye. It just seems so damn unnatural.
Your thoughts?
Probably stinky! You can close your eyes to avoid the eye. But the stink will remain – lights on or off! 
When they have a penis. That pisses me off every time.
Asylum I laughed so hard i thought my lungs were going to come out through my nose!
But seriously (getting back to the OP): Stupidity
Which, i guess, would make intelligence my biggest turn-on. (sorry for the hijack)
Biggest sexual turn-off? I guess decapitation. Kills the mood just like that.
When current standards of hygiene are not closely adhered to.