Shadowcaster
Noun: An involuntary erection whilst sitting fully clothed capable of casting a noticable shadow on the torso of the offender.
Having beers around the fire one night Quinton popped an absolutely absurd Shadowcaster.
shadowcast
A group of actors who get onstage to do a performance of a movie while the movie itself plays on the background, therefore casting shadows on the screen. Also, the performance of same. First started by The Rocky Horror Picture Show, other movies that are often shadowcast are REPO! The Genetic Opera, Hedwig and the Angry Inch, Phantom of the Paradise, and Dr. Horrible's Singalong Blog.
I dressed up as Graverobber to go to the shadowcast of REPO! The Genetic Opera this weekend and got mobbed by scantily-dressed women.