Making sure someone will not succeed or pass.
My teacher pulled a Gandalf today when he gave out a quiz that I surely "shall not pass".
The car in the other lane next to me pulled a Gandalf for about 2 miles. He made sure I wouldn't be able to pass.
Bob: Damn, that girl at the end of the bar is looking fine, I think I'm going to try and make a pass at her.
Charles: No way man, she pulled a Gandalf already on 3 other guys who tried me make a pass at her tonight.
Question: Why didn't the chicken cross the road?
Whenever a girl and a guy are fooling around and things get very hot but all of the sudden she stops foreplay and does not allow penetration. Obviously the guy stops after her "Thou shall not pass!"
"Man I am really in need of having sex with her"
"Did you not have sex with her yesterday?"
"No, she Pulled-a-Gandalf"