1. They don't need to make an effort to cheer you up.
He/she is the answer to most of your miseries. They don't even have to make an effort to cheer you up when you're upset, happiness for you comes naturally with them - gossip, girl talk, boy talk, all talks.
2. They understand your senseless addictions.
It took you ages to make him/her understand WHY you're addicted to a particular thing. Finally, you can say it out loud and this person will never mind it. You don't want to go through the whole process all over again because you know how horribly tough it was to talk about your weird addictions - partying, food, running etc.
3. They know your darkest (and stupidest) secrets.
You'll have to kill them if you stop being friends with them because the kinds of things they know about you, noone else should EVER.
4. You do everything with them - things that you won't ever do alone.
You won't even get out of your house without them (at least when they're around) so imagine the wild things you'd want to do and the only person you can think of doing it with is he/she. Only because he/she is around, you're able to do everything you want to do without any embarrassment - like acting hysterical when you catch the bride's bouquet at a wedding.
5. They have keys to almost everything that belongs to you - house, room, treasure box and ALL YOUR SOCIAL MEDIA ACCOUNTS.
They have direct access to your life. You'll be incomplete without them taking advantage of that fact.
6. You share every embarrassing detail of your life with them.
They'll be good listeners almost every time you need them to be even if it does not make any sense at all.
7. They know a little too much about you.
Despite knowing each and every thing about you, he/she is you BFF. You may not get another because the world is prejudice and it's not easy to make friends, forget best friends.
8. You laugh with them when you're supposed to be serious because you can't stop yourself.
Be it a class or meeting, if they're around, they'll be ready to crack you up at any point of the day. It's difficult to be serious around them but that's the fun part of your relationship.
9. He/she makes even the worst phase of your life so much fun.
Why you go to them when you really need to talk to someone is because you know they won't ever feel 'sorry' for you, they'll make fun of it instead because that'll make you forget whatever happened in a jiffy.
10. You've planned everything you want at your wedding with them.
Since you've told them everything you expect out of your wedding, you want them around to make sure you get your bachelorette party as you expect it to be. You both look forward to each other's wedding days and you know she'll be happier than you on THE DAY of your life.
11. They know all items in your closet by heart.
They can never say "you're wearing the same thing you were wearing the other day" to you because they know you can say the exact same thing.
12. You are dependent upon them completely.
You need them at every baby step that you take in life. Sometimes, he/she really comes across as a second mom to you because of how protected you feel when they're around.
13. You can be your ugly natural comfortable self in front of them.
They never judge. NEVER. You can send them the ugliest snapchats and they'll respond with even uglier ones. The uglier you can be in front of them, the better the friendship.
14. You love waking up with them.
It's the nicest feeling when the first thing you see in the morning is his/her face because that means your day starts with lots of laughter and fun.
15. You will always be on the top of their priority list.
There's no way they'll ever cut you off for anyone in the world and neither will you because he/she is everything you've ever imagined a perfect person to be who deserves a lot more than you can ever give him/her.