Confusing use of とたん in 「来たとたん何か用かよ」


The speaker is experiencing unusual levels of politeness after visiting the
house of a relative who wants them to do a favour (he didn't visit with the
knowledge that she wants a favour):

> 「来たとたん何か用かよ」  
>  _As soon as_ I came can I help you?

I'm not sure which part I'm failing to understand. I was sure とたん meant 'the
moment that'/'as soon as'. And I thought that 何か用か meant 'can I help you?',
but when I put the two together it makes no sense at all.




While " ** _Can I help you?_** " is one good way of translating
「何{なに}か用{よう}かよ？」 in some situations, this is not one of those situations.

Here, something like " ** _So, you want a favor, eh?_** " would fit much
better.

> "As soon as I arrive(d), you want a favor, eh?"

I should perhaps mention the fact that "You want a favor (or something), eh?"
is a far more literal TL of 「何か用かよ？」 than "Can I help you?" is. The latter is
a fairly free translation.

That is because the 「よ」 part of the 「かよ」 ending makes the phrase feel/sound
more like a statement than a question. 「かよ」 adds a mildly exclamatory or even
accusatory tone to the sentence.




While " ** _Can I help you?_** " is one good way of translating
「何{なに}か用{よう}かよ？」 in some situations, this is not one of those situations.

Here, something like " ** _So, you want a favor, eh?_** " would fit much
better.

> "As soon as I arrive(d), you want a favor, eh?"

I should perhaps mention the fact that "You want a favor (or something), eh?"
is a far more literal TL of 「何か用かよ？」 than "Can I help you?" is. The latter is
a fairly free translation.

That is because the 「よ」 part of the 「かよ」 ending makes the phrase feel/sound
more like a statement than a question. 「かよ」 adds a mildly exclamatory or even
accusatory tone to the sentence.

