Yeah - this. In every apartment I've ever lived in, every single person that a tenant doesn't know gets this question - "What suite are you in?" - from another resident or will ask it themselves. It's usually a weird sort of introduction that you have to apologize for, but in my experience, people don't explode with rage and anger. In every case I've been involved in, whether it's me being questioned or me asking someone else, there's a recognition that it's being done out of concern for the security of the building. So it's kind of an agreed upon 'there's a reason I'm asking' thing. There's always an apologetic "Had to ask..." follow up. Always. Maybe I live in civil society, where people feel obliged to look out for one another. Or maybe we're all just filthy racist busybodies. I don't know whether it's an American thing (I live in Canada) but these awkward incidents are very often your first introduction to a fellow tenant. I do know that if I were to ask someone I didn't know and they responded with "None of your fucking business", I'd be asking my fellow tenants who invited the stupid ignorant asshole into the building. Then, when I knew that tenant was out of town, I'd break into their apartment, steal a single item of obvious sentimental value, then shit in their fridge. That's being a real neighbour.