Is いったい (ittai) a “rude” expression?

Question

The expression いったい (ittai), as in

君はいったい何がほしいの

I translated as "What on earth do you want?" with the help of good ol' GT.

1) Is that correct?

2) Is the expression いったい which GT translated as "on earth" considered a "rude" expression?

Answer 1

いったい is not rude unless you make it rude. It has no inherent rudeness within it, but because it carries a fairly strong notion that one doesn't know what's going on, it can be seen as rude if you direct it at someone to express frustration. Like you say, I always liken it to the English phrase "on Earth," as in "What on Earth are you doing here?" This sentence could be read in a friendly way or a rude way, depending on context, intonation, etc. But I don't think it's inherently rude, but rather strong feelings of puzzlement are often used in rude ways.

A more neutral usage in Japanese would be like, for example, you heard a loud banging sound outside your house/door/wherever, and you said いったい何が起きたんだろう？ which I would translate as "I (am strongly perplexed and) wonder what on Earth happened?"