... when you see a girl at a rave who's got pink hair and has a pinkie pie plushy tied around her wrist and you chase her through the crowd so you can hug her and tell her you're a pony girl too! The the two of you jump up and down while you talk about how much you love ponies, become facebook friends and then go to raves together dressed up as ponies.
.... when your favorite T-Shirts all have G1 ponies on them... and you wear them ALL THE TIME.
.... when you don't just have a pony room, you have pony villages you've built for ponyville and they are taking over a separate playroom for the kids, your hallway, the kids room, your basement plus your own pony room for you, the grown up.
... when you name your pets after ponies, and make custom ponies that you name after your children for your children. I made a Princess Eleanor and Princess Isabella for my two daughters.
.... when your have your own pony websites showing off your ponies and customs
.... when you own a log/list of all the ponies you own as a checklist so you can keep track of what you have so you can make sure you have one of ALL OF THEM.
And my all time FAVORTE way to know you're addicted to ponies .... is when you have a dream that you are riding a Pony Llama named Cha Cha through the mall and when you wake up you can't remember if Cha Cha is real or just a dream, then two days later your dad shows up with an old lunch box he found in the garage from your childhood and inside is your long lost my little pony friend Llama named Cha Cha and she's in MINT condition and you're sitting there wondering how on earth you just had a PONY PROPHECY that you would find and rescue Cha Cha from the old yucky lunch box!
Then you tell her how terrible you feel that she was trapped in that old lunchbox all that time, give her the spa treatment and then put her in a special place on your shelf!
LOL - yeah I'm a pony-addict. I admit it.