Mostly seen in FPS and other games, a nicklamer is someone who copies a clan tag or someone's name. Obviously retarded, and only used for gaining attention.
T3h_LOl entered the game, T3h_L0l entered the game.
Original person: "Wow, we got a nicklamer."
Nicklamer: "Your the nicklamer."
Other people: "Wow it's T3h_LOl! Your fcking awesome!"
Original person and Nicklamer: "Thanks."