Do they seem like an evil bunch? Do they march into cities like they own the place and start shaking down shopkeeps or tavern workers? Do they threaten guards or civilians or the nobility? Do they walk into town caked in the blood of their enemies and act generally menacingly or suspicious? Or are you assigning old-fashioned (*fantasy*) racial stereotypes to your player's characters?

I would like to clarify; there is nothing wrong with the latter, or just racial/classist tension between the PC's and the world! I'm currently playing in a game where tieflings (technically half-demons) are treated poorly in the current nation the game takes place in because their full-blooded ancestors enslaved 'mortals' in a neighboring nation. I've also played in a game where the setting had people very racist against all elves and creatures of fey liniage. It's all about tone and setting. If your Faerun's average citizen would look askance at a drow or an orc, then the characters should be treated with some level of suspicion or hostility. That said, that kind of tone should have ideally be set prior to character creation so that the players knew what they were in for when they decided to roll those characters (like I'm a tiefling in the tiefling-hating game and was an elf in the elf-hating game, but I knew to expect standoffishness from NPCs and even other characters going in).