I have developed a bad of habit of just agreeing with people when they are speaking Japanese and I have lost the flow of the conversation. I just say "yes, yes" or take my cues from their face and smile or frown accordingly.
This meant that I told a guy who worked on the boat out to Mishima that I was married, and only managed to just catch myself before I said I had a baby!
Most recently I was shopping with my friend Eriko, who is Japanese. The shop assistant was talking to me about the prints of the bags they have - they are all special and limited editions and stuff. I was beginning to not understand, but I just kept nodding and smiling. Eriko though knows the limits of my Japanese so she knew I didn't understand the shop assistant anymore. So Eriko told the shop assistant - but I understood Eriko when she said it!