Used as an insult. If you say someone is ‘spare parts’ then you’re calling them
useless, or they’re so poor at what they are doing that they might as well be doing nothing.
In a co-op video
game, if there’s someone in your
party that ends up doing jack shit for the team, then you’d say they are “spare parts.”
Player 1: Dude, player 3 got no absolutely no kills the entire
round.
Player 2: I know, right? He
just sat on his ass the whole
game!
Player 1: Yup—he’s spare parts.