Two stories.
1) my wife knew I was small but she thought it was 15cm (about 6''). One day at the sex shop, she bought a small dildo that was 12cm, explicitly stated on the box. She said she wanted to play that I was the stallion compared to it. It ended up, it was as long as mine, but fortunately mine was much thicker, so she was satisfied in her comparison game.
2) always my wife, during university, she was sharing a flat with two girlfriends. One of them was hooking up with a guy with a quite large cock. She bragged to the other two girls that she measured it and it was 20x16cm (about 8x6 in). When they broke up, apparently the girl was complaining he was too stupid, my wife hanged out with him, also attracted also by the size, and she measured his cock to check if what the friend said was true. It was true. They met for about 6 months when she decided to stop. Afterwards, also the third girl hooked up with me. I am so fucking jealous of this story.