There isn't one single reason why girls (or anyone) pose with their tongue out; the gesture can have a variety of meanings.
According to one source, the gesture of sticking out one's tongue has multiple interpretations:
- Rudeness: It can be a sign of disrespect or defiance.
- Disgust: It could indicate dislike or revulsion towards something.
- Playfulness: It might simply be a lighthearted, silly gesture.
- Sexual provocation: In some contexts, it can be used to flirt or convey a sexual message. The reference compares it to eye gaze which "can be aggressive to an enemy, but eye gaze can also be the height of intimacy." Just as with eye contact, the intent changes the message.
Essentially, just like a look, the meaning is heavily context-dependent.
