In high school first gym class we were all lined up in the lockerroom naked being told the procedure in the showers. It wasn't much comparing but everyone saw each other nude.
About 3 weeks later we are at a party of about 8 girls 20 guys and one of them asked about it. Next thing you know these girls have us all lined up, embaressed and our pants down as they look and discuss our sizes, giggling as some of us got hard, touching and making sure we were all fully hard and taking again about our sizes, comparing us and then taking me down to one end of the line and said he's definately the smallest, come on guys match then up whose the next smallest... and lined us up from smallest to biggest.
We spent the next 2 hours naked, the girls were spending most of their time fondling the biggest guys, but would make sure we were all still hard, by giving us a few strokes every now and then. At one point a girl everyone knew I had a huge crush on said it's so tiny I can't tell if it's hard. She stroked me a few times and I couldn't help but cum and get even more embaressed. After that she turned to my friend who was the biggest and said so my sister says you guys like it if we put our mouths on it... none of us had ever had a girl touch ours before this. She grabbed his big cock and led him into the bathroom. By the end of the night 12 guys had got their first blow job, the 3 biggest got 2.