1) Scream and shriek loudly and tell them you're speaking Mermish.
2) Always speak in a British accent (if you're not from the UK)
3) Relate everything they say to the Harry Potter books & movies.
4) Crowd their inbox with HP-related emails, and make sure the subject are misleading.
5) Give them Harry Potter merchandise for their birthday and demand they treasure it forever.
6) Pretend you can do magic.
7) Yell "Crucio!" or "Avada Kedavra!" if they insult Harry Potter.
8) If you're late for something, blame it on your broken Time Turner.
9) Sort every person you meet into one of the Hogwarts houses.
10) Say "Lumos" every time you turn on a light, and "Knox" whenever you turn it off.
11) If you're asked to retrieve something, shout "Accio" loudly.
12) Refuse to wash your hair, and tell them you're going for the Snape look.
13) Spend hours at a time trying to get your broom to fly.
14) Tap all brick walls you see with an umbrella.
15) Demand to know what exactly the function of a rubber duck is.
16) Carry around a hip flask and refuse to drink anything anyone offers you.
17) Hum the Harry Potter theme all day.
18) Talk to animals and insist they're Animagi.
19) Walk up to random people and ask them if their initials are R. A. B.
20) Tell them they're as smart as Grawp. Then refuse to tell them who Grawp is.
21) Scream "THE DEMENTORS ARE COMING!" whenever it is foggy or cold outside.
22) Point at modern electronic devices and say, "The things these Muggles come up with..."
23) Grunt a lot and insist you're speaking Troll.
24) Go to a CD Store and make them help you look for the newest Weird Sisters album.
25) Draw round glasses and lightning bolt scars on every picture you see
26) Complain about how your pictures don't move.
27) Say "Alohamora" whenever you open a door.
28) Say everything in a sing-song voice, and skip wherever you go, like Luna Lovegood.
29) If they ask you about the weather, look up and solemnly say "Mars is bright tonight."
30) Draw the Deathly Hallows symbol on everything.
31) When playing chess with them, give the pieces verbal commands.
32) If one of the Harry Potter movies is on TV, remind them every five minutes.
33) Force them to watch the Harry Potter movies with you.
34) Quote HP when it makes sense. Like if they say they think they're going crazy, say "You're just as sane as I am."
35) Refer to your rivals or people that annoy you as "You Know Who"
36) Start swatting at the air, and explain that there's a Wackspurt in the air.
37) If they ask for your phone number, tell them it's 62442.
38) Ask them to help you study for your O. W. L.s or N. E. W. T.s
39) Walk around bumping into walls and tell them you're looking for the Room of Requirement.
40) Run up to old men with long beards and say, "DUMBLEDORE!! YOU'RE ALIVE!"
41) Tell them their nose resembles Voldemort's
42) Ask all red-heads you meet if they're related to the Weasleys.
43) Call them a "bag of dungbombs" when they bother you.
44) Attack them and claim to be under the influence of the Dark Lord.
45) Make hissing noises whenever you see a snake and say you're speaking Parseltongue.
46) Offer to pay for their lunch... In Galleons
47) If they ask what you're doing, say "I solemnly swear that I'm up to no good"
48) If they ask you to hand them something, say you can't because Lockhart made all your bones disappear.
49) Tell them you're the Chosen One and watch them try to figure out what that means.
50) Complain that your dog doesn't have three heads.
51) Spray them with water and say that you've mastered the Aguamenti charm.
52) When they shake someone's hand, gasp and shriek, "You've just made an Unbreakable Vow!"
53) When climbing stairs, say, "It's a good thing they're not moving now"
54) Call your TV station and ask them why they don't broadcast Quidditch games.
55) State a random fact & when they ask how you know that, say "Honestly, don't you read?" in a Hermioneish voice.
56) Tell them not to block up your fireplace because your friends are coming over.
57) If they say they are hungry, ask them if they want to go to Honeydukes
58) Wear different color contacts and say you're going for the Mad-Eye look.
59) Make turnip earrings.
60) Warn them that if they kill any spiders, Aragog will come looking for them.
61) Burst into tears every time someone mentions the name Fred.
62) Remark on how strangely Muggles guess.
63) Claim all your stuff are Horcruxes and scream every time they touch one of your things.
64) Open all the windows and claim you're waiting for the mail.
65) Constantly remind them that you're a witch/wizard.
66) When they insult HP, yell, "You foul, loathsome, evil little cockroach!"
67) Whenever you hear someone say "I'm serious." say, "As serious as Sirius Black?"
68) If they ever talk about Harry Potter, correct them on everything.
69) If you are shopping with them, suggest to go to Weasleys' Wizard Wheezes.
70) Tell them their teeth resemble Wormtail's. Then don't tell them who Wormtail is.
71) Tell them even Hagrid has better-looking hair than them.
72) When having a joke-off or Yo Mama smackdown, use only Harry Potter jokes.
73) When playing a sport with them, look around, and when they ask what you're looking for, say, "The Snitch, of course."
74) Say you want a pet for Christmas. When they ask what kind of pet, say, "Oh, I don't know...maybe a hippogriff, or a baby dragon, ooh, or maybe an owl."
75) Name all your stuffed animals/pets after after animals in Harry Potter.