What you say when you don't want someone around. Namely the Cedric Diggory(ies, s?) of the world. Found in Harry Potter and the goblet of fire.
and more importantly, in the internet cult favorite musical, A Very Potter musical.
Harry/Darren: 'Cedric, seriosuly, screw off. You're just this spare guy who noone wants around. You're such a spare! "
Quirrel/Voldemort/Brian/Joe : KILL THE SPARE! AVADA KEDAVERA!
A phrase uttered by Lord Voldemort as an instruction for wormtail to kill Cedric Diggory
A phrase now used to advocate the removal of a fat, unatractive or generally undesireable girl from a group of otherwise good talent
Black Dog: Hey man these chicks we hooked up with are smoking, except that fuggers bitch
Titan: Yeah man, Kill the Spare!