It's presumptuous of anyone to demand an explanation for not getting an invite. Friends should appreciate that an invitation is a privilege, not a right.
You might want to include a request to attendees: Please don't post photos on Facebook; let's enjoy this party in the moment.
Tell these social media sleuths that there wasn't enough room this time or you were cultivating a certain group that would all get along.
You don't have to explain yourself to them. Just let them know that it's not possible to invite everyone to every gathering.
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