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There may be something more precise than what I'm remembering, but here are some:
One-Person Birthday Party if the character is throwing a party but no one shows up. Locked Out of the Loop if a party got cancelled and no one told a character. May also come with a tumbleweed for comic effect.
There's also Late to the Tragedy, Slept Through the Apocalypse, or Humanity's Wake for more epic situations of this kind.

A character arrives to a location that they expected to have people in it, only to find it empty. For example, someone attends a party that was cancelled without their knowing, or a child comes home to find their family gone. I'm sure I saw this just a few days ago, but I can't find it now.