You don't have to call them every day, just to let them know you're not fighting
You don't have an anniversary-you just sort of "became" best friends.
When someone calls your girlfriend/boyfriend your "partner" it makes you think of marriage. When they call your best friend our partner, it's more like cops.
You never have to touch your best friend when it's hot outside, but you can still huddle close when it's freezing.
Your parents usually like your best friend.
Your best friend doesn't care if you get fat, you're ugly, or if you get a ard haircut.
You don't have to get jealous of "girls only" night or "guys only" night -- You're part of it!
You can laugh at your best friend with no consequences.
You can burp/fart in front of your best friend on any occasion.
You can plan on still having a relationship with your best friend in 20 years.
Never in your life will you need "space" from your best friend.
Your best friend won't be mad if you want some time alone, and will only ask you "what's wrong?" once.
Your best friend is someone you get in trouble with; your boyfriend/girlfriend is someone you get in trouble with if you get in trouble.
You don't have to get dressed up to go anywhere with your best friend.
You're allowed to have multiple best friends.
No one ever spreads rumors or talks about you and your best friend's relationship.
Borrowing any amount of money from your best friend is okay, no questions asked.
Your best friend will never refer to you as "the ball and chain," "the old lady/man," or "the whip."
No one is ever trying to fix you up on blind dates for a new best friend.
It doesn't matter what your "other" friends think about your best friend.
Your best friend is the first person you call when you get a new boy friend / girl friend, and when you break up with them