The excerpt that illustrates situational irony in Saki’s "The Storyteller" is:
“‘It’s the stupidest story I’ve ever heard,’ said the bigger of the small girls, with immense conviction. ‘I didn’t listen after the first bit, it was so stupid,’ said Cyril.”
In this passage, the irony lies in the fact that the children express strong disdain for the story told by the bachelor, yet the actual story that he tells contrasts with their criticism and ends up being more engaging than the aunt's attempts at storytelling. Their vehement disapproval of the "stupid" story makes it ironic that they are dismissing something that ultimately captivates the reader's interest, illustrating the reversal of expectation.