A Low Ping Bastard, or LPB as it is called in-game, is one who has an excessively fast internet connection, thus reducing the ping between his/her/its computer and the server or the host. These people naturally experience higher frame rates (the number of times the screen refreshes per second. The more times it happens, the more fluid on-screen movement you get. If it's low, the action on-screen is jerky.) than the rest of us, and thus appear to be better players. But that is not the case. They just have a better internet connection that makes them look cool online.
To combat this problem, people have set up varying servers with set internet connection speeds (e.g. 56K, DSL, Cable). If anyone's ping happens to be out of proportion to the rest of the players, they would be removed from the game.
Some particular games that suffer from these people are Unreal Tournament, Counter-Strike, and Half-Life.