During the summer of my thirteenth year, my family would take a few trips to the beach. The beach was an hour or so drive away from the suburb we lived in. At home, I had already changed into my light blue swim briefs, so when we got to the beach all I had to do was take of my shirt and shorts and I was set!
During the car ride, the unusualness of wearing swim briefs under regular clothes while riding in a car gave me a nice boner from time to time. At 13, I was probably only two or three inches soft and four or five erect - not super long but I was still proud of my tiny weeny!
At the beach, I wasn't much of a water person, so I stayed on the sand and took off my clothes to rest and tan myself. My parents and sister went into the water. When we arrived, it wasn't too busy but after a while the beach was packed. There were soon many families who set up their towels and umbrellas close to my family's.
Next to me, I saw a hot looking boy about my age, wearing red tight-fitting swim briefs. He was gorgeous with a slightly muscular body and I popped a full boner straight away. I tried hard to get my mind off him, but I couldn't stop staring and my boner wouldn't go down. I was super horny now and wanted to jerk off, but where? Sure there was the beach change rooms, but that required a few minutes walk and everyone would see my obvious boner in my swimsuit.
Panicking slightly, I turned my body over so that my boner was pressing against the towel. Instinctively, I started to slowly hump the towel, trying my best not to move too much so as not to draw attention to myself. After a few minutes of this, I realised I had gone too far to stop. Rope after rope of cum left my penis and splattered in my light blue swim briefs, creating an obvious wet patch at the front.
I remained in my position in embarrassment. I knew I had shaken my body a little, but to my relief no one seemed to paying any attention to me. Phew! To rinse out my swim briefs, I quickly ran towards the water to join my family, who were surprised to see me. I looked back towards the boy in the red swim briefs and soon I had a boner all over again...