The tone comes from Skype for Windows, the desktop version of Skype, the internet calling and messaging service that became a household way to make video and voice calls. The error call sound was the system's way of signalling that a connection had failed, so users heard it during dropped calls, busy lines and unsuccessful attempts. As clips from old software interfaces became popular in edits and reaction videos, this short alert was reused as shorthand for rejection and technical failure, which is why it still works even for viewers who never used Skype itself.