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 get a broom for Christmas. 

Every time you turn on a torch you mutter "lumos" under your breath. 

You sort everyone you meet into four categories. (Gryffindor, Ravenclaw, Hufflepuff and Slytherin.) 

You had to go to the hospital after you broke your nose running headfirst into the wall between platform's nine and ten. 

You try to turn your brother into a bouncing ferret. 

You collect plugs. 

You try on ever piece of silvery fabric your mum has to see if you turn invisible 

Before getting up to get something, you always try to summon it first. Accio!

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 poke pictures in the house hoping to make them move. 

You try to find an article by Rita Skeeter in the newspaper. 

You go to antique stores searching for a clock that tells where people are.