Is it rude to make các câu hỏi about users?

Its REALLY rude,

But without them knowing hoặc finding out

If they know about it beforehand and they say it's okay,and as long as the các câu hỏi are not too personal it should be fine.If they don't know about the questions,then yes,it is kind of rude.

Not really, I tell bạn its perfectly fine! Except to just go to the right place to do it! c:

It depends. Though, it's better to just not make các câu hỏi about other users.

Well I guess it just all depends

Depends on the question.

if it isn't insulting, inappropriate, hoặc done with the wrong intentions/outcomes then i believe it is fine

I would say it is.

If bạn have a câu hỏi about a specific user, just ask them privately rather than putting them on blast.