I'm posting this after making a comment on the reckless dice podcast about the happenings in an adventure they're running. There are some minor spoilers for the adventure.
Basically, a player was playing a wood elf PC in The Gathering Storm, and decided that an ambiguous character they met was a beastman and shot at him. Although this character is a beastman, the adventure takes care to make him out to be not outwardly a beastman and mentions that PCs may think he's a human. The player had read the adventure before and thus knew about the NPC being a beastman, which leads to the question of whether he was sort of meta-gaming the situation. However, the context does make it a possibility that the NPC is a beastman. This is further complicated by the fact that this "metagaming" wasn't actually meant to give the player an advantage, but rather just to roleplay his character hating beastmen.
For those who didn't read, a player in the adventure arguably used out of game knowledge about the adventure/game world in a somewhat ambiguous situation. My gut instinct upon hearing this would be to have the player roll a Lore check to see if their character has that knowledge. However, I'm then left with whether it would be okay to forbid the player to have his PC act on the knowledge if he fails the roll. Essentially, is it okay for a GM to forbid a PC to do something if s/he thinks the player is not roleplaying his character correctly?
I can see arguments for both sides. On the one hand, it's a player's right to play their character however they want, and the fun of a roleplaying game is that you get to attempt wacky things you come up with. On the other hand, if a GM is basing a story on a PC's established knowledge and behavior, is it wrong for a player to not roleplay his established PC? Is the established character in the narrative as important to play as the numbers on his character sheet, and if so is it cheating to not play that character?
Another related issue to this is players not playing to the numbers on their sheet (brilliant player plays a PC with 2 Intelligence and has them come up with lots of great ideas). I think this issue has already been hashed out plenty of times, however, and I'd like to see what people think about players acting against what their character should know/is established to act like.