Pair the Spares is a term used to describe the act of pairing together secondary characters, usually with little relation to the overall story.
Example of Pairing the Spares
Cartman and Kyle are left in the cold. Still, both of them have experienced the pain of heartbreak and unrequited love — so why not hook them up together? They may not have any initial attraction to each other, but they can always hang out and reminisce about their similar failed romances, and somewhere along the way, they might just find mutual love with each other like their former partners have.
It could also be the case where Cartman and Kyle were paired together to act as a secondary pairing (and foil) to the primary relationship.