(slang, noun, Among Us):
A dig at a player that is acting suspicious, but is otherwise definitely not The Impostor.
This “Crewmate” player may be failing to complete their tasks, accusing the wrong people, or not voting in line with the majority. Although they aren't necessarily killing anyone or trying to lose, their chaotic playstyle makes them seem like a mini-Impostor, or if you will, a “third Impostor.”
Impostor A: Charlie was the greatest 3rd Impostor I could've ever asked for.
Impostor B: I can confirm, greatest 3rd Impostor.
Charlie: Drumsy didn't even have anything on me, and he was ready to vote me off because I was being so ridiculous!