Stupid Questions

Wendy and I had a good chat + catching up yesterday over dinner and after dinner hours about our life and relationships. Both of us were caught in this topic:

What's a guy's definition of "stupid questions"?

If a guy tells a girl: "I haven't been in a relationship for a long time already.." or anything like that, automatically a girl will reply asking: "How long already?"

I've encountered such situations before and I must admit the first instinct I had was to ask how long. Then either the guy answers me how long or just a I don't know or he comments it's a stupid question cos he doesn't know how long?

:/

Sometimes questions come with a set of questions as reply and sometimes a sentence can result in a question too. How do we girls know whether it's a "stupid question"?

Please enlighten me..