This happened a few years ago when I was about thirteen or fourteen. I remember being upstairs and going into my room. I had shorts on and a t-shirt, and my mom said she was going to start the water in the bathtub so I could have a bath. So she went into the bathroom and I lay down on my bed for a few minutes before it was ready.
Well it wasn't too long before this I discovered what masturbation was. So I put my hand down my shorts and started to feel around and in no time it was hard as a rock. I lay down on my tummy and started to push it and rub it against the mattress. It felt so amazing that I kept going and going, even harder as I started getting closer to orgasm. I hadn't been cumming for long so it was really exciting whenever I did.
I started to hump the mattress because I was really into it. I knew I was about to cum in seconds. Well I guess I didn't hear the water turn off because all of a sudden my mom popped her head into my room, she was saying something like 'It's ready...' when she noticed I was on my stomach thrusting my hips against the bed. I didn't notice her at first because I could feel the cum shooting out all over my underwear and shorts. The orgasm was so intense as my muscles contracted in my dick. I'm sure seeing my body shake was an interesting sight. I looked over and just caught her head backing out away from the door. I felt sooo embarrassed that I didn't leave my room for the bath for like fifteen minutes until she had gone downstairs. We never talked about it again, and it was awkward between her and I for a while.
That was the only time I was really fully caught. I should post my first time with a guy another time. This site rocks!!