Fifth Friend Syndrome

A negative social effect in which a new person in a friend group usually thinks he's friends with the people in the group. And tries his hardest to integrate into their social structure. But the people in the friend group usually treat him as a friend. But in reality, they're doing it not to upset him/her. They usually treat the new person like a dick. Acting nice while also putting him/her in the background.

Usually named so because the new person mostly tends to be fifth one. Most social structures consists out of people in groups of 4.

John: "I asked Kevin if he would want to hang out some time. He said yes but he just straight up ignored me after I tried to ask him when but he ignored me. At the end of it he hung out with another friend and completely ignored me."

Bob: "John, it looks like you have fifth friend syndrome."