I have a brother who is a year older named James. He's pretty attractive at 6'2', slim.
One day several years ago when I was 14 and he was 15, just the two of us were home. We were both watching TV in the family room at night. We were in pajamas which meant just boxers and a shirt for him. I had been used to seeing him dressed like this so it was no big deal. During a commercial, he said I was going to the bathroom and got up and walked to the bathroom. My eyes followed him and I was shocked when he didn't close the door. He just popped his dick out of his boxers and started peeing at an angle that allowed me to see everything. His dick looked really big as his stream of urine exited it. Once he was done peeing, he just gave his penis a couple of shakes and put it back in his boxers. He then flushed and left. He noticed me staring at him so he gave me a smile. I couldn't think of anything to say except: 'You didn't wash your hands.' To that he replied by taking his dick out again and shaking it at me from across the room. He chuckled, covered himself, and sat back down to watch TV.
At the end of the show, he took the remote and told me he was finding a better program. He went up to the movie channels and stopped on a channel with soft-core porn. I was too dumbfounded to say a word. I just watched him as his dick slowly grew in his boxers. Then all of a sudden he took out his hard, enormous cock and started masturbating! I couldn't believe my eyes. I just watched as he rubbed his dick until he came and sent cum all over his chest. He then got up without saying a word, cleaned up, and returned to watch something more PG rated.
The next morning, while I was brushing my teeth, my brother walked into the bathroom completely naked and announced that he was showering. We have a glass-enclosed shower, so I could see everything. I 'brushed my teeth' long enough to see him jack off and cum. He did all of this not looking at me, make it look like he didn't care at all that I was there, just like he did the night before.
That was the beginning of an interesting relationship. Since then, he's jacked off in front of me thousands of times and exposed himself in many other instances. He randomly whips his cock out and jacks off. I remember I was talking to him about which college I should go to and he took out his dick and we had an intelligent conversation while he was masturbating. He even waited to clean himself up until we were done talking.