American Sign Language:  "immature"

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In this version of "immature" you use your "pinkie."  Hold your extended pinkie off to one side of your nose. Move your hand sideways brushing your pinkie past your nose. Use a double movement.
Note: you don't actually have to "touch" the nose. 

IMMATURE:

 

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IMMATURE: Version 2:

There is another version of immature that holds an "i" against your non-dominant palm and slides the "i" downward a couple of inches while changing the "i" into an "M"-handshape.