The one who seems so innocent but actually secretly holds a knife and just appreciating its sharpness until dawn. Insanely SARCASTIC, too. Did I mention she's the Queen of Badasses.
She may be looking like an angel but she's literally the Demon of demons.
A dirty Julie is a giant orgy consisting of you do a handstand against the wall twerking and getting fucked in the ear with a 1 inch wonder while one or more of your friends watch from a far eating shrimp alfredo and yelling Yahtzee!!!