A dirty bennelli is when a girl is having Intercourse with a man that as a long very long penis. The next day if the girl says "I had a dirty bennelli" it is a form of having great sex, and hoping to get back with him again.
Girl had a Dirty bennelli last night and let me tell you he was huge! Like a foot or I don't know 14 inches! I am so going back to him for more.