The infamous moment in Harry Potter and the Order of the Phoenix in which Remus Lupin and Sirius Black hold each other's gazes for a length of approximately forty lines. Used frequently as evidence by Remus/Sirus shippers.
A: Remus/Sirus is so canon!
B: No it's not!
A: Yeah, it is! Check out the Forty-Line Stare in OotP!