10.

Follow Ghost Hunters around, but only do things that are easily explainable without a "ghost" hypothesis.

-BolthMC

nah, follow them and when they freak out at some random noise and ask "what was that?" appear beside them to answer "gee, I dont know"

-butterscotchchat

9.

I'd possess the Biology Class Skeleton, march to the front of the room, and scream,

"I GOT A BONE TO PICK WITH YOU, EH HEHEHEHE!!!!"

-daodmwip

8.

Go on their phone and rearrange their applications on the home screen

-MADDA_2078

I'd have your spectral @ss exorcised so fast...

-LaBelleCommaF

That is the evilest thing I have ever heard...

-Banayonet

7.

Oh man I fantasize about this all the time.

The usual opening doors and moving car keys around. No light flickering, that gives the game away, but turn out lights in vacant rooms. Rearrange books or DVDs or records, just slightly. Put a frozen meal in the microwave, but don't turn it on. Change the TV channel when they go to the bathroom

Fold their laundry, or put it away. Rearrange decorations on their walls and shelves. Replace light bulbs that burnt out.
Little things. Things that make them think they're going a little crazy, or losing their memory. Going senile, even. Keep it up and personalize to the hauntee. They'll never even know I was there.

-jankgreen

So you want to redecorate and maintain basic upkeep to my home?

-Product_of_purple

Pretty much, but in a more spoo^ooooky way.

-jankgreen

6.

If they're decent people, I'd find things they lost and put them somewhere they can't miss it. Phone missing? Boom, it's on the chair. Keys gone? Hanging out of the lock. If they forget to grab their towel before a shower, I'd set one out for them. And maybe I'd whisper poetry to them when they sleep.

If they're assholes, I'll wake them up about an hour before they're supposed to get up, either by blasting early My Chemical Romance over their Bluetooth speakers or by growling the Verse of the Ring at them in the original Black Speech. (It sounds intimidating enough to possibly be a demon, and my Latin and Aramaic need work.) When they finally relax enough to go back to sleep, I'll turn off their alarm.

-LaBelleCommaF

5.

I made a pact with my best friend growing up that the first of us to die would come back as a ghost, and then throw a book so we could tell who it was.

So I'm going to go to her house and throw all her books at her.
She'll love it. She's cool like that.

-2FootCircus

4.

I'd hard boil some eggs
Give them an ice bath when they're done
Peel them
Throw them in a bowl
Chop some green onion
Throw that in a bowl
Put some mayo in the bowl
Mix it good
Bring out the bread
Make egg salad sandwiches
Leave them out and the people living in the house would be like
"Sh*t, who made these man?"
It'd be an instant classic

-sad-doggy

3.

I'd tap the shoulders of people walking next to each other and make them stare at each other with weird looks

-UnPhayzable

Listen here satan....

-HuluAndH4ng

2.

Move random objects slightly so its enough for them to question if they left it like that but not enough to be sure that they didn't.

-BaldHeadSlick

1.

Set their toasters on the highest setting.

-Wajirock

You monster

-BlameSociety1