The warning in the title is the whole joke, using reverse psychology that makes listeners want to play the clip precisely because they were told not to. Sounds with this kind of dare title spread on soundboards and in group chats as dares, pranks and reaction clips rather than as actual phone alerts. Its thirteen second length helps the gag, since a real ringtone is usually short and ignorable. It remains used because the setup is instantly understood, even without knowing the original context, and the payoff is the awkward attention it creates.
About this sound
A loud, attention-grabbing clip jokingly labeled don't use this as a ringtone, shared as a prank sound effect for reactions, edits and fake call moments.
This clip is built around the joke in its name, turning a normal phone alert into something far too loud, long and attention grabbing to use in public. At just over thirteen seconds it keeps going well past the point where a ringtone should stop, which is exactly what makes it funny when it plays unexpectedly. The effect is instant embarrassment and confusion, with everyone nearby looking around for the source. It works best as a prank sound rather than a real alert, dropping a moment of chaos into an otherwise quiet scene.