A totally awesome religion in which the practice consists of eating lots and lots of pistachios and having other people mooch pistachios off of you.
The bigger your mound of pistachio shells on your desk, the more impressive and / or hungry you are.
Also commonly done instead of work that we should probably doing, mainly in Science class.

Founders of Pistachioism : Annie & Michele
( because we are that cool )

To refer to a member of the opposite sex in conversation when such discussion may be considered overly discriminatory or sexist when being overheard. Can refer to the USDA system of grading for pistachio nuts and shells (i.e. U.S. Fancy, U.S. Extra No. 1, U.S. No. 1, and U.S. Select).

To fuck a girl so hard you leave her quim chafed and red to where it resembles a pistachio.

look like beans, smell like nuts, feel like shell, sound like nothing, taste like heaven.

Used as a literal replacement for "That's what she said" in times when the full statement would be deemed crass and boorish, e.g. when in the presence of your grandmother.

The Single most addicting snack ever

they look like little green penuts but DO NOT BE FOOLED!

they are really little green alien seeds sent to earth so that once one becomes addicted and eats enough they will explode and little alien babies shall run free...

Thee aliens plan on harvesting the seeds in 2012

A delicious nut snack