When you scratch 'Nimbus 2000' in your regular old broom at home, in the hopes that will make it fly.
When, after you've seen the film and read the book, you try to use the 'Wingardium Leviosa' spell to levitate paper with your pencil, and when you can't do it, think you're saying it wrong.
You've seen the film at least ten times in the theatre, and enjoy it more every time you see it.
You believe JK Rowling writes about Hogwarts from her own experience.
You can hum the soundtrack in your sleep - and at sleepovers, really drive your friends mad.
You act out random scenes from the film in the middle of class at school - very loudly - and at a time when nobody else is talking.
You dress up in wizards' robes and dark glasses and etch a scar on your forehead and push through the queues at cinemas yelling, ''Move aside! Don't you know who I am?!''
You've dressed up as Harry Potter every Halloween since you can remember, and you still do - even though you're 23 years old.
You trot around telling people (very loudly) that your last name is Potter (even though it's not, or maybe it is) and that yes, you're related to THAT Potter - he's your second cousin.
You've bought at least two copies of the books, one for reading over and over and over, and the other for sitting on the shelf and looking beautiful.
You have the British version of the books, as well as the American version, the German version, the Spanish version, the Italian version, the Latin version, the Japanese version, the Dutch version....
You have a VERY serious crush on one of the actors that played in the film.
You visit Harry Potter fansites many, many times a day, looking for anything new in the news about Harry.
You memorise the lines from the books and the movie and you even memorise the spells and stuff.
When you go to school, ask people if they like Harry Potter or not, and when they don't, attempt to put a spell over them.