A psychological effect, induced by name dropping certain video games, that causes anyone who played that game to have a sudden urge to play it.
Named after the 2000 PC game Deus Ex, which famously will cause at least one person in the conversation to reinstall the game whenever mentioned, especially online.
Fred: Hey man, did you ever play that Deus Ex game? It was totally awesome.
Bill: Oh yeah, I loved that game! I should install it on my new PC.
Fred: Aw man, now I wanna play it!
Bill: That's the Deus Ex effect for you, buddy.