Also, it's showing that we don't take whatever it is seriously. It can be a part of playing and joking, but also a part of distancing ourselves from something or someone.

As for why it sounds the way it does, that's probably just a small trait that randomly got amplified and entrenched by evolution, just like smiling when happy or crying when emotional. Body language isn't nearly as changeable as language, but it still deviates quite rapidly when species differentiate. Just look at how differently dogs and cats use their tails, or how apes show their teeth in very different situations than humans.