Best Friend

How you guys define a best friend?

Some conversation happened between me and my friend and make me THINK really deeply about how to define a best friend.

Me: " Hey.. Are they couple ? "

( Well.. is kinda boring in the class so I need gossip to cheer up myself )

Friend A : " NONONO ! The aren't. They are just best friend. yea.. just best friend. ( 3 seconds later ) Well.. Maybe a little little of over the best friend line."

Me: " Ou.. Then how you define as best friend ? How are they over the line ? For example ? "

Friend A : " Alright.. They....... A always go to pick up B, every morning and going to breakfast or having meal together. So... "

Me : " OU !! So that's how you define a best friend. "

Then I gonna have dozen of best friend. ( eyes rolling )

Well.. I really a bit of pissed off about this answer. It is not what I expected.

Anyone of you having a GOOD answer ?