I believe there is such a thing as getting comfortable at first sight.
It's when you only just met this person and you could just talk to that person like you've known them all your life -- you're simply open when you'd normally wouldn't be.
Yun bang tipong di ka nahihirapan?Realized that me and one of my friends were that way. As in I've never really talked to her before, but when I did, a steady stream of jokes, insults (my signature), and opinions just flowed out with no inhibitions and the same way happened to her.
I dunno, I think it's one of the things that complicate us humans.