This goes back to when I was about 14 years old. I was at home jerking off in the powder room on the main floor of our house. It was a weekday afternoon and I wasn't expecting anybody to come home at that time, and I had left the bathroom door slightly ajar. Just as I started cumming, I heard the front door open, my father was home. I reached for some toilet paper and managed to wipe up most of the mess, and as I was zipping up my pants I could hear my father asking who was home. I replied, and he told me he needed me to help bring in some groceries he had picked up.
Thinking back, I should have run the tap so I could wash my hands in the sink, but I was feeling very guilty and not thinking straight. I exited the bathroom and was surprised to see another man standing there in the foyer. As I walked past them my father told me that it was a new salesman he had just hired, and told me to shake hands. I reluctantly reached out and shook the man's extended hand.
I'll never forget the look on his face as he grimaced and brought his hand up, palm outstretched and fingers spread widely, his eyes scrunched up and his nose wrinkled as he tilted his head to look for the source of the unknown moisture. My father took no notice and I turned and headed out to the car to bring in the groceries.
Years later, watching an original episode of a science fiction series, the memory came rushing back as I watched characters on the screen getting infected by a disease passed by hand-to-hand contact. As I watched a crew member grimace and raise his hand to inspect it, I began laughing uncontrollably as I imagined his hand contaminated with my sperm. In fact, even though I'm not gay, every time I see someone inspect their hand in a similar fashion, I imagine that my semen had somehow ended up there and they're wondering what it could be they feel on their hand.