Although this happened a decade ago, I am still "beating" myself over it and felt like I should get it off of my chest. Back when I was 14, I was masturbating like no tomorrow. Once or twice a day for about two years, I would beat the meat in my bedroom and then proceed to ejaculate all over my carpet. I was a lazy kid and didn't keep a box of tissues in my room. I also liked to see how far I could shoot my cum, so being the sensible kid I was, I decided just spewing my load on our carpet was the best option. Let me point out that although we had carpet, it wouldn't become crusty or white or anything like that, so I wasn't worried about my parents seeing. When I was 14 we also had a cat who was 18 at the time and having some issues controlling his bladder. After two bouts of him pissing on our floor, my parents decided to find out where he was pissing, so they researched how to find out if your carpet has cat piss on it. They found out that under blacklight, cat pee glows in the dark. They ordered a blacklight off of the internet and then decided to scan all of our carpet right after the got the blacklight while I was at sleep away camp. When I got back the a week later my dad seemed off in the car back. Apparently while I was gone, they found that the cat had peed all over my room and decided it would be best for them to put him down while I was gone, to spare me the trauma of having to say goodbye when I came back, and also wanting to put him out of his suffering. I was sad at first, but then I thought that was a little strange since my beloved cat didn't hang out in my room very much because it was in the basement and quite cold. Wanting to see how bad it was, I waited until my parents went to sleep and went downstairs with the blacklight to check it out. My carpet had around 50 or so splotches of glowing stains on it and then it hit me. Those stains were my jizz. My parents must've thought it was cat pee and put the cat down before I could explain what it was. I was overwhelmed with guilt and sadness, but eventually when I was older, realized it wasn't entirely my fault. To this day I have told no one, so this feels real good to get off of my chest.
TL;DR: I was came all over my floor. Parents mistook it for cat pee and put my cat down. Note: Sorry for bad grammar and run-on sentences.