At the time I was about 6'2' and 200 lbs. My dick was probably 6 in.
In my junior year of HS, I travelled around my home state and some bordering ones to see colleges. Most of the time I just went with my dad for day trips, but when we went to PA, my mom and brother tagged along. We stayed in a cheap hotel and had two rooms: One for my bro and me and one for my parents. I jacked off nightly back then, so I need to jack off that night, even if my bro was in the room. I snuck lotion into my bed with me to use as lube and I quietly applied it to my dick under the covers. I slowly stroked my dick until I couldn't hold off any longer and threw my covers off and came all over my stomach. I thought my brother was sleeping so I got up, without any pants or boxers on and went to the bathroom to clean up. Turns out he was awake and he followed me into the bathroom to see what I was doing! I explained and told him not to tell. Luckily he did not tell.