On topic, I did this only once in my life. I was in my senior year in high school. Finally got this girl I've been trying to get with since my sophomore year. For whatever reason, she was extra horny this day and came over to my place after school. I use to have these black out curtains on my window, so my room was extra dark. I remember reaching down there and saying "damn baby. you wet already." SHE DIDN'T SAY SHIT. The only thing that gave it away was halfway through (yes we were already in the act), I thought something wasn't smelling right. Pretty much killed my mood. I acted like my family was coming home soon so we had to wrap it up. I walked her out, came back to my room, and got back in my bed. My bed was wet as hell. My dumb ass thought i was the man and made her o face a few times. I turned on the lights to see my light blue sheets all fucked up. Took the sheets off and it already made a slight stain on my mattress. Went to take a shower and it looked like my dick had been ripped off. We saw each other the next day and said nothing. I don't remember talking to her for the rest of the year. lol
tldr: Due to a high school experience, I know i'm not into period sex.