Don't smoke next to someone else's van, especially mine...............there are subtle ways to get the message across, like with a hose.
Yes as an ex smoker I think you notice it even worse, probably wont be long before we see smoking in van parks banned as is the current trend when you are within so many metres of public building entrances etc, certainly parks with close sites would qualify to have to meet those rules.
Apart from most of the things already mentioned I have a couple to add,
Encroaching on others sites with your car, boat, awning or general crap, if you wish to use part of my site then pay for it!
Crossing through sites, especially on awning sides and I dont care if you have to walk and extra 10mts or 50mts to get to the toilets, shop, beach or your new friends down the other end of the park, think of my site as toll road, if you want to use it then leave your money on the fridge.
Not plugging your power, water sullage into the correct outlet, and then inadvertently turning off someone else's services when you pack up by mistake.
Leaving a flood on the basins in the toilets, how hard is it to keep the water in the bowl.
Various toilet mistermeaners and worse, really are you a civilised race or straight out of the trees.
Don't leave your old hair cover soap, empty shampoo bottles, soap wrappers etc in the showers.
If you do laundry then don't leave t in the machine/dryer for hours after the cycle has finished, I usually put it on the bench but I will eventually start dropping it on the floor as I don't like doing my own laundry let alone someone else's.
I've got a heap more but now I'm just sounding old and whinny.
Life member of the GOB club.