Doing extra-ordinary well, or even just "doing great" or "doing very well". Usually, "it" in "killing it" refers to some kind of game, so they're "killing the

Doing extra-ordinary well, or even just "doing great" or "doing very well". Usually, "it" in "killing it" refers to some kind of game, so they're "killing the game", or doing a really good job beating the game.