I remember this happening back when I was 14 years old.

I was at my friends house and his sister and one of her girlfriends was there. My friend was 13, his sister was 15 and her friend was 16. The sister's friend pulls out a porn magazine. We all began looking at it and there was mostly naked women in it with just a few men. My friend tells the girls to take their clothes off so we can see their pussies. His sister says us guys should take off our clothes since there were not many naked men in the magazine. The sister's friend said she would get naked if everyone else did. My friend says there is no way he was going to get naked and his sister said the same thing. The sister's friend suggested we all strip down to just our underwear instead then. My friend and his sister said they wouldn't do that either. She turns to me and says she would still do it if I do it too. To my friend's and his sister's surprise I did it and so did the sister's friend. I was in just my underwear and she was just in her bra and panties. My friend and his sister began shouting at us to just take everything off. The sister's friend said she would but only if everyone else did it. Of course my friend and his sister reused once again but tried to get me to take off my underwear. I flashed them my bare ass which caused everyone to laugh. I did it a few more times and got the same reaction but had their mouths drop open when I just went ahead and took them right off. I stood there naked before them and the sister tried to get her friend naked too but she still said she would only do it of everyone did. I was the only one naked and for my first time ever being naked in front of others didn't feel the least bit shy or embarrassed. I must been naked for over 2 hours and the friend staying in just her bra and panties for that time too. One time during this period my friend left to use the bathroom and his sister went to answer the phone that rang. Being alone with just the sister's friend she showed me her tits and slipped off her panties briefly giving me a look at her ass and pussy. It was a very good spread look and exposure of her pussy. She said I earned the look for getting naked. When my friend and his sister came back they had no idea she had done that. We eventually got dressed as it was getting close to dinner time.

Nothing happened with us like this ever again even though it would have been interesting to see the sister's friend again or what it possibly might have led to.