When you are invited over for dinner... is it rude for the host to tell you to bring a bottle? NO.. I don't think so.. however when you say - OK I will bring wine and beer... then they turn round and say - no, bring vodka is that OK with you?
Is it really OK?

Personally, I wouldn't care. I'd bring whatever I was asked to. And if I wasn't asked to bring what I really wanted to, I'd probably just bring it in addition to what I was asked to. I'm almost never asked to bring desserts but I like desserts and usually bring one anyway. Maybe your host is planning to make a special drink for you and the other guests and needs vodka for it?

No I don't think so... just know that the host and her husband like vodka here and there!

Well, it's pretty common to bring things you know people like. So I still really don't think it's a big deal that they asked you to bring vodka. If it's really bothering you that much then why don't you talk to them about it? Other wise going at all seems like a bad idea if you're going to be stewing about this the whole time. That'll just ruin the whole night for everyone.

If you are a guest to someone's dinner then the host should not ask you to bring anything, unless it's a potluck. Its customary for a guest to bring something if they like, and honestly it looks rude if you don't. I think it is rude for them to ask you to bring something and to be specific about it. Its almost like them thinking you do not have the common courtesy to know better or to bring something good and appropriate.

It also depends on how they said it. If they need the vodka for something specific then that's not rude... but if they were demanding or bossy about it then its rude.