elevating small talk to medium talk

What is the line that people cross from small talk to medium talk?  How does one know that the talk is no longer small?

This really is a good question for a conversation over thinker like myself.  On another somewhat non-related note, yesterday I said, "By all means!" with gusto to some stranger on line at the Post Office, and for the next 15 minutes that I waited on line, I went over that stupid little phrase and wondered what possessed it to come out of my mouth.

Because who really says, "By all means!" in real life, with gusto?  To a stranger in line.  Apparently I do.

I admit that at about 12:30 am, when I was laying in bed thinking about whatever I usually think about when I can't sleep, that dumb moment came to mind. Ugh.

So anyway, small talk.  Is it the content?  The amount of time spent talking?  How do we know??  What are the actual rules??

And while we are tackling this subject, is there a large talk?  A vente?  What's the cut off before it just becomes talk??