Teenage girl: Sally.
Male person: Wait, wasn't Jared your best friend last week?
Teenage girl: He's my best friend too, but Sally's my BEST friend.
Male person: So what about Haley?
Teenage girl: Oh, she's my best BEST friend.
Male person: ... Okay, what about Susan?
Teenage Girl: Oh, HER. She WAS my best friend until she wore the same dress as me to Chris's party last week. Susan! Wearing the same dress as me to my best friend's party! I mean really!?
Male person: *walks away confused and with a drop of at least 5 points in his IQ level*
2 Girl best friends: They do all the girly things together, no one says anything.
2 Boy best friends: They do all the boy stuff together, no one says anything.
1 Boy + 1 Girl best friends: They do boy and girl stuff, People says lots of stuff
Gun Man: I’m going to kill your best friend miss
Stu: No take me instead!
Your real, true best friend is your comfort zone.
In some cases, the two or more part doesn't apply. It is quite possible to be your own best friend.
You have ''in'' jokes that no one else can get, but you still find as funny as ever =) You don't have to pretend around them, they like you for who you are.