Number One: The Bathroom.
And I don't mean the snooping around looking in medicine cabnets...I am not a stalker. I mean is the sink clean, is there mold in the tub, and would I be scared to sit on the seat in this bathroom. There have been plenty of guy's bathrooms where I have seriously contemplated "hovering" or "nesting" (ladies, ya'll know what I'm talking about, where you put millions of layer of tp on the seat cause its gross

).
Number Two: The kicthen
The sink and the fridge. If the sink has dishes upon dished upon dishes that looks like it hasn't been done in weeks, that creeps me out. I can deal with a pot, some plates or utnesils or something like that. If the fridge has some nasty green crap all over the food, that is disturbing too.
Other than those two things, as long as there isn't dirty stuff around (ie. a plate with last night dinners on the floor by the couch) I'm okay.
Litterboxes in visable areas kinda skeeve me too.