The 'UU? RR?' meme originates from the Twitch streaming community, specifically popularized by the 'Brian' text-to-speech (TTS) voice used by streamers like xQc. Viewers discovered that typing specific combinations of letters, such as 'UU' and 'RR,' caused the AI voice to produce a rhythmic, percussive sound that sounds like a repetitive grunt or beat. It quickly became a staple of 'TTS spam,' where viewers use it to create chaotic auditory environments or react to high-intensity moments during a live stream. Today, the phrase represents the unique, often nonsensical subculture of Twitch chat and the interactive relationship between streamers and their audience.