The Dirty Gandalf is the art of masturbating on to the Chin of your partner, creating a messy white beard of spooge, they must then shout "You shall not pass!". To add extra credibility to the act, midgets dressed as Hobbits may be used as well as other props like robes, staff etc. Photographs must me taken for posterity.
Darling , I have ordered midgets for tonight, get your robe on, its time for DirtyGandalf to arrive.
When a lad requires the assistance and guidance of a lass in order to pull some fit piece of ass, the lass in question is providing the role of vaginal gandalf
It is when you are titty banging a girl and blow on her chin. This gives her the distinctive look of that magical white wizard that used to pal around with hobbits. Next, tell her to get a towel, point to the wrong door (the one that leads outside,) lock said door, and leave her outside so that the "magic" freezes to her face.
I saw that Gandolf Glacier he gave her. Obviously, he chose to go through the mountains rather than brave the Mines of Moria.