Annoying things guests do

We're not talking major infractions here, just small stuff that makes you scratch your head and wonder why.

Unplugging all the lamps
You might chalk this up to people being conscientious about energy usage.  But given that the same people will go out and leave the ceiling lights on and the heating turned up/cooling turned down, I don't think that's it.  And no, it's not to make room for their rechargers because each outlet has a free socket.  Any ideas?

Going through the linens closet
I've had guests leave the linens closet looking like Macy's after a major sale: everything in disarray. And often they don't appear to have taken anything out, they just wanted to have a look through your stuff.  When guests do help themselves to the linens you've got a problem on your hands - not enough clean towels/sheets for the next guest. Putting a 'Private' sign on the door helped but didn't completely stop the behavior.

Rearranging the cupboards/furniture
This might be more understandable with longer-term guest, but I've had the contents of the kitchen cabinets completely rearranged by people staying only 2 nights.  I find dining chairs in bathrooms and out on the deck but the problem hasn't been as bad with the furniture, probably because it's heavier.  Still, it's no picnic having to return to the living room (by myself) an armchair that it took 2 people to move to the dining room.

Running a full dishwasher cycle for one cup, one plate, and one fork
In my experience, it's only Americans who do this.  Also annoying, leaving a sink/dishwasher full of dirty dishes or leaving their cleaned dishes for me to put away.

Leaving the front door unlocked
Okay, we're moving away from the annoying to the potentially dangerous here.  Do you really need to tell grown-ups to lock the front door in a city?

So, what's the most annoying thing you've had a guest do?