Yeah I never know what to say at the time. My brain works best when it's had hours/days/weeks/months/years to think things over and come up with a constructed response. I constantly re-analyse conversations I've had from throughout my life and think up better or more accurate (to how I was feeling) responses.

I think it's probably why I prefer online interaction. If somebody says something which you don't know how to respond to straight away, you can take your time to think it through and analyse possible responses before saying anything. If you did that in reality, people would think there was something seriously wrong with you.