The guest who knows less should not have to become smaller.

In a room where everyone shares the references, the person who does not ends up doing extra work: laughing along, waiting to ask, quietly deciding not to. Not knowing something has been turned into a small deficiency they must apologise for. Good hosting moves that cost off the guest and onto the room, which is where it belongs, since the room made the shorthand in the first place.

When you are the one who knows, supply the missing half-sentence before anybody has to request it. Name the person you are all referring to, explain the joke lightly, keep the thread reachable.