It seems to be strange to open up a thread of the worst milage on an Insight, but keep in mind that for a lot of people it could be great mpg.
My worst ever mpg was on December 15, 2000 when work was closed early so people could go home before the roads iced up. It was not soon enough. I was going 30-40 mph the first 30 minutes. After that, the ice and sleet turned all the roads into a stop-an-go parking lot going at 2-3 mph. The rest of the trip was four hours. Over 30 miles, I got 25 mpg. The defroster prevented autostop from working.