The closest I've come to a "haunting" was at Le Meridien Cambridge-MIT. I think it was the 3rd floor, one of the basic rooms with two queens, in the bathroom.

The way the bathroom was structured was that you enter the door, and the sink and mirror is to your left, and the toilet bowl is in front of you; and the bathtub-with-shower is to your right.

It was the second day of my 2-night stay, and I was taking my first shower at night after a day out. As I finished, I pulled the shower curtain apart, and as most of you are familiar with, the mirror was fogged up... except... there were the handwritten words "I WAS HERE." that showed up while the rest of the mirror was fogged. This didn't happen the day before, and my door was bolted, the mirror looked perfectly clean and normal when I entered the shower (I usually wash my face first, because it gets annoying when it fogs); and I was the only occupant of the room.

However, being a scientist, I didn't really care if a ghost or a person did it, what mattered more was how it was done. I was very impressed by how well it was done. I assume the mirror was cleaned, then some hydrophobic astringent was used to write over the mirror. Common of cosmetic products and some bathroom products to have an alcohol-water medium that evaporates, depositing a thin film of the hydrophobic organic molecules that aren't visible to the eye unless very closely scrutinized. And when the mirror fogs up, the parts where the film was deposited show up clearly over the rest of the mirror.

So I tested my hypothesis, cleaned up the mirror, got some Le Meridien conditioner, diluted it with the running water over my hand and used my finger to smear the words "I HATE QUANTUM FIELD THEORISTS" over the mirror. When it dried up, you could barely tell that there was stuff on the mirror. And it worked, though I didn't do as clean a job as whoever/whatever did originally. But I guess it's interesting to share this so you guys don't get a rude shock if someone/something plays this scare on you.