Like many here, I have never not gotten a reaction to seeing my cock for the first time. And just to note, the first time reactions are the absolute BEST! Removing my clothes or her taking off my clothes and out flops a cock that isn't hard but already significantly larger than an "average" erect one is sure to get some pretty interesting comments.
My most favorite reaction was playing strip black jack with two female friends. They had both lost and were completely naked, while I still had articles of clothes on. One insisted that we keep playing until I was naked which didn't bother me. When it finally came time to take off my underwear, my cock dangling and swinging as I took them off to which one said "DAMN simbablk" while the other said something similar and giggled almost nervously. After a few minutes (or so it seemed) of them admiring my big cock, one whispered in the ear of the other something. She nodded in agreement and told me that I had lost and therefore had to do whatever they told me. I chuckled and asked what that was. She lied back, opened her legs and told me I had to eat their pussy. Of course I obliged and got my face down there and went to town. At one point, I got on my back and had one riding my face and motioned for the other to suck my cock. That began my very first FMF threesome which was fun but extremely exhausting as they made it clear early on they weren't in to doing things to each other. But still, it was my most favorite since I got to experience fucking two women at the same time who both enjoyed my big cock.