Quilladin. It's those eyes and the blank stare it has in the games. Quilladin looks like a psychotic killer with a creepy stare that will stab you to death as you sleep. Much like this:
Oh damn, I'd have to say magmortar (its face or lips just...ehh), and slurpuff (it looks like a creepy candy addicted kid who never leaves the candy store).
Greninja's 'scarf'.
It being it's tounge just grosses me out. I always wonder if it ever gets dry or if it touches you, would it be slimy? And would it hurt to tie it around Greninja's neck? Just that tounge part creeps me out...
Sigilyph just always creeped me out. I have no idea what it's based off of, but it doesn't look like it can fly far with those flimsy wings. Also, it seems to have many eyes staring at you, ehhhh.
But, like always, these are my opinions. You may disagree and agree as you please.
Cubchoo - you've got a cold, don't touch me.
Beartic - snotcicles, need I say more?
He looks like he wants to do more than battle you...
Oh gawd yes! That should be on my list too!