A small square of dried translucent substance containing a ‘hit’ of acid, that is, LSD, and resembling a ‘gel’ used in theatrical lighting. It dissolves in liquid, melts in your mouth.
A form of acid from the 70s. It came in colors (pun intended) such as amber and brown. Hence the name Amber Windowpane.
In order to protect oneself from being punched, you can call Security or just say a simple "Excuse Me".
Other derivatives of Safety/Doorknob include Tent Zipper, and numerous others I can't think of right now that are more appropriate to a particular situation.
Spencer: Window Pane!
(Spencer beats the crap out of Josh, until Josh stands up - especially amusing in class - and touches a window pane)