My mother and I were invited to a party, on arrival we found there was not a lot of seating available, but we found a chair in the corner of the room, mum said to sit down and she would sit on my lap, things were fine for a while but she started to wriggle to make herself more comfortable, that is when it happened, I got a raging erection I am sure she felt it as she wriggled more and my cock was struggling to find some room inside my pants, trying not to think too much about the situation I failed and had an almighty orgasm, I could feel the cum filling my pants, and mum must of felt the warm sticky goo on her, surely enough she got up and there it was the evidence of my orgasm had stained her dress.