A person (F1) who, when in a friendship, plots against one of his friends (F2) with another friend (F3). They (F1 & F3) exclude the second friend (F2) from activities like going to someone's house, to parties, or to any location that it is possible to enjoy oneself.
Also describes a person who talks behind his friend's back. See Gossip.
Kanive (adj.), Kaniving (v.)
Matt: Greg and Corey rented Dynasty Warriors 5 and played it without me. They are Kanivers.