The unwritten rules of friendship. Never have a relationship with someone your best friend has feelings for. Never sleep with your best friend's exes, no matter what they say. Even if they say it's okay and they approve, don't do it if you are a true friend. And if you do, you're not a true friend.
Stephanie had strong feelings for this guy she once pretended to hate, yet her best friend completely overlooked this by disobeying the best friend code and having a relationship with him. Now they are no longer friends.
When you're really close with a member of the opposite sex and would like to date them but they refuse to date you because you are too close and they wouldn't want to make anything awkward between the two of you if the relationship didn't last.
You have best friend syndrome if...
1) You hang out with the person of your dreams more often then your friends. But ARE NOT dating.
2) They ask you to take them to an STD test or a gynecologist appointment. Or go with them as moral support to get Plan B (even though you weren't the one to have sex with her)
3) Other acts that a boy friend/girlfriend would do minus the sexual benefits, emotional attachments and etc.
Mother: So hows Andrew doing? I'm sure hes not too happy you dumped him for Josh.
Daughter: Are you kidding?! We were never dating, he just had a bad case of Best Friend Syndrome.
The ability two or more close friends have when they've been friends for a LONG time. They tend to know what the other(s) are thinking, finish each other's sentences and communicate using almost no words.
More common in female best friend relationships but not limited to them, inside jokes could be one of the reasons why best friend telepathy occurs.
BFF 1: Wow, our best friend telepathy is getting ridiculous
BFF 2: I know! I didn't even have to say more than two words and you already knew what I was talking about!