My first time was with a friend who was engaged to be married. She apparently had a thing for me years before and was getting it out of her system. I ended up fucking her twice that night. I even went down on her. I never realised she was on her period until I got home and saw the look on my housemate's face. I don't think she knew either. I wasn't invited to the wedding.
The second time was with partner number two. That involved messy oral and penetrative sex.
I have also fucked a friend's wife on her period. She was so horny and we did it bareback a number of times.
A friend has fucked my wife on her period too. I have a pic or two of that, and can post here if people want to see (I know some get grossed out by blood).