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).
"Check out the pistachio by the doorway. Extra No. 1 grade."
by shabazzier January 5, 2017
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.
"It was hard"
by rtac April 29, 2008
A woman of loose moral character.
Further, a woman that one takes home for the night.

Coming from the Ludacris line "I was with some nasty ho's eatin' pistachios."
"Alright, you can have the room tonight, I'll sleep in the lounge. Just make sure that this pistachio doesn't touch any of my stuff."
by PH Loom June 1, 2007
to urinate. from colloquial-"piss"

"pat, i'm busrting for a pistachio"
"mark, i'm not surprised with all that beer you drank"
by mark n pat September 11, 2003
To fuck a girl so hard you leave her quim chafed and red to where it resembles a pistachio.
I pistachioed the ole lady's snooch real good last night.
by wolfbait51 May 7, 2011
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
by Troya! October 19, 2008
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 )
Instead of doing Physics work in the back row, we all practice a little Pistachioism instead.
by Annie and Michele March 19, 2008