Party of one??

Hellow everyone.
My question:
What "Party of one" means?
If you knew it, tell me, thanks.

補充

There are two persons, A and B.
They're talking each other, and C appears.
C: Hello, A.
C leaves.
B: Freak. Party of one.
B said that to A.
Update: Thanks for your replies.
You're so great.
5 answers 5