Sorry, if it's too short, but that's all i could think of.
1. Go to him and say "I know what u did last summer and i'll tell Ron." and see what his reaction is.
2. Poke him with a wand of a stick and when he turns around, pretend it wasn't you.
3. Tell him he has his mother's eyes and his father's package.
4. Laugh hysterically every time he walks in front of u and when he asks why whisper "I've read your diary." then run away. Still laughing hysterically.
5. Ask him how his parents are.
6. Ask him if Dumbledore has proposed yet.
7. Write an erotic story about Snape and Harry's mom and read it to as many people as possible as loud as u can in front of Harry.
8. Follow him around and after a while whisper in your coller "The boy isn't noticing us my Lord. Code 1521." and make sure he hears you.
9. Every time u see him with a girl make Hermione/Ron/Drako/luna/Dumbledore etc. go and slap him then make them yell "I thought there was something between us!"
10. Sit volgende to him in cless and do annoying stuff lkie blowing your nose and throw the used tissues on him, make origami swans and purposely make mistakes then throw them on him and start new ones.
11. Ask him dumb vragen like "Where is Chuck Norris?", "Do u like waffles?", "What's your favourite colour?", "Why is the sky blue?", "Are u team Edward of team Jackob?", "Why did i saw u sneek up in the girl's bathroom last night?", and ask that until he goes nuts and yell at u then say with an innocent voice "I was just asking."
12. Ask him if he watches "Bold and the Beautiful"
13. When he goes to bed say "Can i Slytherin?"
14. Point to a random guy and tell Harry "I think u to will make a great couple."
15.Give him annoying notes with a lot of grammar mistakes especially "your" instead of "you're" and vise versa.
16. During an important test make "psst" noises and ask him to tell u the antwoorden and when he turns around say "Hey, no peeking!"
17. Drop somethimg on the floor and whep he tries to pick it up yell "Hey that's mine!"
18. Ask him what's the time every two minuten until he goes nuts.
19. Make him play "Barbie" game all day.
20. Play the song "Friday" door Rebecca Black as loud as u can and when it ends ask him "Do u like it? It was on your MP3 player!"
21. Ask Harry "Have u read Twilight?"
22. Ask him if he has read the "Harry Potter" books.
23. Ask him if he knows J.K.Rowling.
24. Make him a dumd theme song and sing it as many times as possible and ruin every single serious moment.
25. Kill Voldemort before Harry and make all seven boeken completely pointless.
26. Ask him several times if he thinks Robert Patinson is hot.
27. Make him say "Gingers don't have soles" in front of the Weasleys.
28. Go with him on a very long road trip and start singing 365 days of the year. The song goes like 12 days of Christmas only longer.
29. Record an entire JB album on his MP3 player and make him listen only to that album.
30. Force him to watch "Disney Channel" all dag long and see if he'll go homicidal.