Yeah, I saw that posted all over Facebook yesterday. My girlfriend tagged her best friend. I don't have a particular individual who I can say is my best friend.
When I was younger, I considered one friend to be my best friend but I found out indirectly back when we were teens and again more recently that they've considered various other people to be their best friend over all these years we've known each other. The more recent discovery was from Facebook posts. I guess people still don't realize that other people can see your conversations. (In fact, Facebook seems to think you would want to read anything two of your friends are saying to each other and just toss it at you.)
In my nearly 44 years, I still have not come across anyone who "gets" me. The sad part of it is I don't realize they don't until they pull away or make some sort of declaration that they don't understand me and question my motives, and then everybody's feelings are hurt. I think the closest I will ever come is those people who, even though they don't "get" me, have come to realize my motives aren't dubious and I have a place in their world as a "friend" but I think becoming someone's "BFF" or "soulmate" or whatever is extremely unlikely.