From Tabletop [=RPGs=]:

This troper once made a character that was an old granny who worked in a shop, only to find herself in an action where she needed fighting skills to get by.

This troper has also seen the opposite, where someone made an action character with an impressive arsenal of weapons for a game that turned out to have no action whatsoever.

This troper has a friend who when I start talking about tropes constantly thinks he's going to be the comic relief guy who gets killed. He doesn't seem to realize we're in Art school and thus in more of a Romantic Comedy/Drama than a Horror movie.

@/DoctorWorm experienced this hard in an ''{{Exalted}}'' campaign. The setting was our world, about 10 years in the future, when people start Exalting. My character, an Abyssal, had been experiencing visions of a titanic figure in black spiky armor, which I (out-of-character) knew was obviously the First and Forsaken Lion, one of the main antagonists of the setting. my surprise when I discovered that this was not in fact the Lion, but ''the [[BigGood Unconquered Sun'', heavily corrupted by the Wylds.]] Yes, it turned out that blood-drinking undead warrior was working for the good guys.

My GM got mad at me for this one. I've been playing video games much longer than tabletop games, and I couldn't help noticing similarities between the party's current situation and the Legend of Zelda games. As such, I had my character act as those games taught me to, and I noted this. It turns out it was very, very different, and my GM told me this. Otherwise, we wouldn't have gone very far (I was the tank, so I would have to go first).

In a Naruto RP / Fanfic of mine, Saga Doshi thinks he is in a grim and gritty Seinen Manga where his actions are acceptable. Really, Saga?

My dad managed to watch the entirety of Saw under the impression that it was a standard mystery film.

In a Pathfinder game, we attributed a description of rumbling and rocks falling to the structure crumbling, due to us dispatching what we reasoned had been a Load-Bearing Boss; in fact, the fallen foe was simply going One-Winged Angel on us. We ran from the not-actually-crumbling structure, in what we thought was a clean getaway in an Indy Jones-esque action sequence...and missed the last chance to slay an evil dracolich-god before it was reborn on the material plane. Basically, we *LOST* the campaign at the last possible second. In retrospect, all the filthy dungeons, blood-engorged abominations, rotting diseases and Faustian deals up until that point really should have told us this final fight was going to be a tad darker.