Steal his glasses

Break them half

Then hold them over his head and tell him to jump for them

Ask him how he got his scar

When he tells you say "woooooowwww, that is the worst looking lightning shaped scar ever"

Sing the chorus of Grease Lightning over and over (emphasize on the lightning)

Steal his wand

Do stupid magic tricks with it like "accidentally" turning people into frogs

Look at it and say "hmm it looks a bit bigger than others, trying to overcompensate for something?"

Steal his invisibility cloak

Follow him around while wearing it and say "wooooooo I am a ghost. I am INVISDDDIBLE!"

Keep saying "Harry, Voldemort is you father" in a Darth Vader voice

Walk around with a fake scar and coke bottle glasses

Tell him to cover his scar with make-up so Voldemort won't recognize him

Ask him if muggles can see his scar

Tell him he sucks at Quiditch

Say "if Voldemort kills you, can I have broomstick?"

Use his broomstick to sweep your floor

Etch your name into his broomstick

Dye his hair hot pink

Ask him how Cedric is

Hide Ginny in a closet and tell him she ran off with Malfoy

Throw the Harry Potter books at him and say "WHEN WERE YOU GOING TO TELL ME YOU WERE A WIZARD!!!!"

Write a fake diary and claim it's Ginny's. Make sure there are lots of pages that say "I 3 Draco"

Make a cardboard cut-out of a dementor and chase him with it

When chasing him make lots of ghost noises

Keep calling him Daniel

Every time he walks in a room scream "AHHHH DEVIL CHILD!!!" then run away

Ask him why he hasn't killed Voldemort yet

Keep telling Voldemort where he is

Ask him if he really did petrify all those people, then make up a ridiculous excuse about a gigantic snake that kills people when it looks at you. Oh and Voldemort just HAD to be involved

Carry around a doll with glasses and a scar drawn on it

Stare at the doll all the time muttering "I love you Harry"

Photoshop a picture of Ginny and Malfoy kissing

Give it to him

Put it on your Christmas cards and give them to everyone you know

Give Harry seven

Replace his glasses with ones without lenses

Send him love notes from Voldemort

And Malfoy

Spoiler (just a warning) Hand him 'Harry Potter and the Deathly Hallows' and say "did you know that you die? Voldemort kills you"

After he has a panic attack say "but don't worry you come back"

Follow him around humming and whistling the Harry Potter theme tune

Get up close to his face and stare at him for ages

When he asks you what you're doing ask "why aren't you as cute as Malfoy?"

Make him read Harry/Ron fan fiction

And Harry/Draco fan fiction

Say to him "your hat's left a horrible mark on your head Harry"

Follow him around saying "he will return tonight" in a really creepy voice

Keep saying "ya mom" after everything he says