Short story about a man betting a group he could tell a story, and one of them would disappear and the others would not notice

In about 1966 or so, a stand-in teacher at our primary school spent the afternoon reading short stories to us. There was a wide genre, but I was particularly fond a one which was science fiction/mystery.

It involved a group of people who were talking about mysteries, and another man from outside the group bet the he could tell a story, and one of them would disappear and the others would not notice. The final line was something like "he kicked over the stool and walked from the room".

Answer

This sounds like Exit by Harry Farjeon (adapted into a film in 2012)

It involves a group of people attending a dinner party including a newly-wed couple by the names of Jake and Jessamy. Mr Geeles claims he can erase people from existence, referred to as "de-creation" in the story. Of course no one believes he can do this, as the de-created are also wiped from all memory of ever having existed. He ends up trying to demonstrate his claim. At the end an empty footstool is kicked over where Jessamy had been sat.