A feeling of disenchantment or a 'letdown' in the atmosphere; when fun or excitement is spoiled and people become apathetic.
彼の冗談が滑って、場がしらけてしまった。
His joke fell flat and the atmosphere went cold.
あまりにも下手な演奏に会場はしらけていた。
The audience was left unimpressed by the very poor performance.
しらけた空気を変えるために、司会者が話題を変えた。
To break the cold mood, the host changed the topic.