From Ask Amy recently. We have a friend who does this and it drives me up the wall. Ever experienced this?
Dear Amy: I have a very close and caring friend. "Susan" is wonderful and generous but does one thing that drives me crazy. Whenever I invite her and her husband to our house, she always asks who else will be there.
She does this before giving her response (which is "yes" 99 percent of the time). She asks this in emails, so I cannot quickly parry her question verbally with: "Who are you interested in seeing?"
What is a proper way to stop this question? I feel that it is none of her business who else I invited. If I am invited to someone's home, I don't ask about other guests ? I give the host an answer about us and that's it.
I feel it is rude to ask this question every time. It's as if she is more interested in seeing my other guests than me and my husband.
Please help. I don't want to lose her friendship but this has been building up for too long. I end up either ignoring this question in my response email or saying I don't have others confirmed yet.
Read her answer and the rest of this here.

Re: Do your friends do this?
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I think I ask this sometimes of people, but it's never meant to mean that I wouldn't go if certain people were there, it's more like I have no filters and that tends to come out before I say yes.
Btw, I read the other questions and the last one is super cute.
Tea Time for Lulu
Yeah, seriously! Our friend likes to gauge if there's going to be single women there. I think he should come because he wants to spend time with his friends. It's so freaking rude.
I have friends that will ask specifics... will X be there? Is X bringing Y? Are there going to be a lot of single men/women? And will there be other people with young children? But not just a random guest list. Generally I am sympathetic to the concerns.
That is annoying and rude. You could just not invite him :-/