You mutter nonsense latin words under your breath.
You call your least favorite teacher Snape.
Your computer says "You've Got Mail" and you run outside looking for an owl.
You actually ask for a broom for Christmas.
You mutter "lumos" under your breath every time you turn on a flashlight.
You sort everyone you meet into the four Hogwarts houses. (Gryffindor, Ravenclaw, Hufflepuff and Slytherin.)
You were burned when you couldn't get through the flames of your fireplace.
You had to go to the hospital after you broke your nose running headfirst into the wall between platforms nine and ten.
The wand order mistake in GoF drove you crazy, and even after it was "corrected" you still came up with dozens of theories to explain why that happened.
You point a normal things like parking meters and say "Look at the things these muggles dream up!"
You collect plugs.
You try on every piece of silvery fabric your mom has to see if you turn invisible
Before getting up to get something, you always try to summon it first. Accio TV remote!
You watched "Love, Actually" because two minor Harry Potter actors were in it.
You were reduced to tears when you finally had book 5 in your hands.
You refer to your Chemistry class as Potions.
You spend hours tapping bricks in special orders hoping that a secret entrance to Diagon Alley will appear.
When playing chess, you yell orders to the chess players and get upset when they don't move.
You yell into the "fellytone."
You get emotional every time you hear "Hedwig's Theme".
You say "wicked" all the time because Rupert Grint does.
You get thoroughly overexcited every time you see a word somewhere that is distantly linked with HP (ie. Saint Hedwig's).
You name all of your pets after HP characters.
You get in to heated arguments over how much gel Tom Felton had in his hair in the first two movies.
You know that Harry's birthday is July 31, 1980, Hermione's birthday is September 19, 1980 and Ron's birthday is March 1, 1980 even though it never said in the books.
You refer to Voldemort as "You-Know-Who", and no one has any idea who you're talking about.
You went out and bought the latest editition of the Webster's Dictionary because they added the word "muggle".
You were kicked out of the movie theater for standing on your chair, throwing your shoe at the screen and yelling "THAT DIDN'T HAPPEN IN THE BOOK!"
You count the days until you're old enough for your apparating license, and everyone else thinks you're talking about driving.
Your free time on the computer is spent constantly refreshing Harry Potter news sites, hoping for an update.