Original.
Seinfeld episode The Betrayal
A [last minute] invitation to an event such as a wedding, birthday, or other gift giving gathering. An unvitation is sent to someone who the [sender] does not want to be present at [the gathering], and with the last minute [notification] they would be unable to attend. The desired result is that the recipient will feel obligated to buy the sender a gift, because they received an invitation, yet the sender does not ever need to host this person.

You were invited
A last minute invitation to an event that had been planned for a longer period of time. The recipient of this unvitation often would have been able to attend the event had they been included in the planning process, but by the time they are made aware of the plans, they can not. The sender often uses this unvitation to deflect guilt by saying But you were invited.

Hollow empathy.
An invitation to a social gathering that is already [underway]. Often the sender of this unvitation is seeking to appear empathetic by inviting a lower status friend who had been excluded. Meanwhile, it is common that the sender knows the recipient is most likely waiting, and hoping for the invite. The sender knows that they could have extended the invitation earlier, but by waiting they received the status bump of being the [recipients] ticket to the gathering. The sender can signal their virtue by having offered the invitation.