fragging (killing another player, from Vietnam era soldiers' slang)
gib (from giblets, the bloody goblets left in the playing field after a player or monster is killed).
A low-ping bastard (or LPB) is a player who has a really fast Internet connection and low "ping" times to the game server, giving him an advantage over (better) players with slower connections.
A buff is a spell or other game effect that temporarily increases a character's abilities; to debuff is to cast a spell on a character that adversely affects his or her abilities.