Example:

She: So why do you want to go out with me?

Me: Because I'm interested in you.


Reality: Obviously both know that you want to go out with her because you are interested, that's not really a question. Is it ever good to state it like this? Let me give another example where it's much more clear that you shouldn't:

She: So why do want me to come over?

Me: Because I want to have sex with you.


Reality: Probably she knows that chances are that it at least crossed your mind, but verbalizing it like this will rarely do you any good.

These were stupid examples, not like I am ever going to answer like this literally that but I just used them to illustrate what I mean. My question is thus, how far is being fully honest good and where is it better to just jokingly answer to the question?