Nope. We don't expect all girls to wear thongs. They have their purposes for certain clothes (removing pantie-lines), and things are almost always exciting to see, but really there are plenty of other types of underwears that are equally sexy for other reasons. Here are a few examples.
All of these have different kinds of sex appeal. I say if you want, wear what you want. You can also experiment with different panties to try what you think is more your style, or what's more comfortable to you. But really I think variety is the spice of life. It's good to have different kinds for different occasions.
No matter what, though, you're not weird for not wearing thongs. You're not even weird if that's all you wear under your clothes all the damned time. It's your style. It's your fashion choice. It's your body. Wear what you like.
Not at all. Not at all times at least. There are situations when thongs are just not what she should be wearing. Plus, how am I supposed to know what she's wearing under everything else? I don't really care unless I know I'll be getting really intimate with her later.
no, it's actually better if some girls don't wear them as they have atrocious asses. I mean my better judgement dictates that I pass on wearing a thong because of the grossness that is called my ass, so use good judgement on it.