Half-Life 2 originally had a part where you go to an arcade where you can play video games but secretly the video games are real and you're killing real people without even knowing, which is so funny like the aliens decided to prank the humans after conquering them.
@tredlocity
@TShockPodcast
has a bit where the main characters go into what they think is a combat training sim but is actually a remote soldier drone interface for culling a warlike culture on another planet.
The aliens who introduced them to it didn't realise they'd think it was simulated.