A way to annoy someone who does not like Harry Potter is to incorporate quotes from the books and movies into conversations. As an exclamation similar to "Wow," say "Merlin's beard!" If the person who does not like Harry Potter is sad, say, "Happiness can be found, even in the darkest of times, if one only remembers to turn on the light." If the person wants to make plans for Friday night, say, "Brilliant! It's Potions last thing on Friday! Snape won't have the time to poison us all!"
Next time you are with someone who does not like Harry Potter, compare as much as you can to events and things in Harry Potter. Say that any plant you come across "Looks like a venomous tentacula." Whenever there is a confrontation between two people, say, "This is just like when Harry defeated Voldemort in 'Harry Potter and the Deathly Hallows.' " If you are stuck in traffic, say, "This would be much faster if I had my Nimbus 2000." If you and the person who does not like Harry Potter are going out to eat, say, "This would have been much easier when I lived at Hogwarts. We could have just had the house elves bring us dinner."
Refer to yourself and the person who does not like Harry Potter as "The Boy Who Lived" and "He Who Must Not Be Named." If you see him doing something that he should not be doing, say, "Mr. Potter!" in a high-pitched Professor McGonagall voice. Whenever you need someone who does not like Harry Potter to do something for you, refer to him as "Dobby" or "Kreacher." Whenever he makes you angry, call him "Voldemort," "Snape" or "Malfoy."
Carry around an ordinary stick and cast Harry Potter spells on things whenever you are with someone who does not like Harry Potter. Stand in front of doors and say, "Alohamora," as if you expect the door to unlock at your command. Whenever the person who does not like Harry Potter gets annoyed, point your stick at her and say, "Avada Kedavra." When nothing happens, say, "Nice defensive spell. You are a powerful dark wizard."