One of the things I hate about sci-fi is that they too often assume that an entire planet is of one stereo-type. When it comes to Earth based stories, most readers consider national stereo-types to be cheap story telling, boring and even objectionable (racist). But when it comes to sci-fi stories, they are far too quick to accept that every person from the XYZ planet to be ruthless bounty hunters, or ABC planet are mentalists and pacifists. I get that it is easier to do this, but this is propaganda level story telling - All Nazis are cruel but cowardly killers, blah blah blah. Not supporting the Nazi cause here, but to assume that every one of your enemies is a certain way is stupid and short sighted.
The same is true in most fantasy games. All orcs are stupid and violent. All goblins are sneaky and underhanded. All elves are tree huggers. All dwarves are grumpy. Lazy story telling!
So how do you do it? How do you convince your players that stupid stereo-types are stupid? One of the best ways is to turn the tables on them. The aldar use stereo-types in their plays and operas all the time. It’s like silent movies - the guy in the black hat with the handle bar moustache is always the bad guy. So what are their tropes? Blonde women are naive (OK, they really think bubble head). Not too different from modern thoughts. Black haired women are lustful, but typically have mean husbands. Elves are also naive and gullible.
How does this help? Well, after being assumed to be brainless barbarians, or bubble-headed blonde morons, or pathetically weak glass cannons who can’t adventure when they have a sniffle, yeah, it tends to get upsetting. Hopefully after being assumed to be a stereo-type themselves they might see that there is a good reason not to return stupidity.
The other strategy is to make NPCs who are direct opposites of the stereo-type. Put in a shirtless barbarian, but make him a healer. Put in a scrawny mage looking guy, and have him turn out to be a dedicated locksmith. Have the female warrior show up in strong armor that doesn’t make her look like a sex pot, and have her able to fight like a ninja despite the weight of the steel. When they see that you are not going to play by the stereo-typing rules, they will know they can’t judge a book by its cover.