I always assumed I was perfectly average. The first two girls I slept with were (really sheltered) virgins, so no comments there. My third girlfriend had been with several guys and she said "wow" when I bounced out of my pants at my fullest. That got me thinking. So later that night when I was alone, I measured it, then Googled the average penis size, and I was quite a bit above. It's still hard to tell whether people mean it or if they're just being nice/flattering your ego though.