GLaDOS is the sardonic artificial intelligence at the heart of Valve's Portal series, voiced by Ellen McLain, whose deadpan put-downs made her one of gaming's most quoted characters. The slow clap, the universal gesture of insincere applause, fits her personality so well that the clip became a staple reaction sound across YouTube, Twitch and TikTok. Creators reach for it whenever a moment calls for mockery without words, and its staying power comes from that perfect match between character and gesture: nobody does condescension like GLaDOS.