My favorite experience was with my friend Sam. I was a sophomore in college, he was a freshman. He is latino, short athletic soccer build. Very hetero, sexually active, and attractive. One morning he was in my dorm room as I was getting out of the shower. He saw my penis and remarked, "Wow dude, it's bigger than I thought." I thought that was a funny way to say it. A week or so later, roles reversed I saw his penis, and he was nervous that it looked "all small right now." Couple weekends later, we are hanging out one night in my room at my parents house, started to watch some porn. I got an erection, and pulled my boxers down to mid thigh to brag a little. Sam immediately stood up on the other side of the bed, looked straight at it, "Dude, that's f*** huge! Look at that!" He ended up lying back down next to me, we both slid off our boxers, lubed up, and masturbated. I remember watching him stroke his penis and watching it get hard. Was about an inch shorter than mine, but thick with a huge mushroom head.
We continued to masturbate together every couple weeks for the rest of that year. Each time, he was openly laughing and comparing our dicks. He wasn't ever shy to look at mine or actively show me his. Kinda stopped for the rest of college, then moved to different states. Almost 10 years after that, he came to visit me. I told him I had just bought some sex toys, and he wanted to see them. I had a penis pump that I dared him to try, he was nervous. So, I pulled down my sweatpants and boxers. "Look, it's small right now, " I said. He looked at my penis for the first time in years, and agreed that that morning I was hanging small. I inserted my penis in the pump, started pumping it and as I got big and hard, Sam's eyes widened. "Dude, look at that! It's so big. And look how big that vein is." He then tried the pump as well, followed by a vibrating cock ring that I had. It was great.
To this day, frequently when we talk he is joking about how big he thinks my penis is.