Akanbe

A Japanese facial gesture, usually considered childish. It consists of pulling down one lower eyelid to show the red inside, while sticking out the tongue. It is sometimes accompanied by the sound べえだ (beeda, pronounced "behhh-dah").

The gist of the the gesture is an infantile taunt - the Japanese equivalent of thumbing your nose at someone, and/or yelling "Nyah nyah nyah" or "Neener neener" or the like.