This reminds me of when I had sex with my ex while she was on her period for the first time. I pulled out, and after seeing blood on my twanger for the very first time in my life, this is what I blurted out: "Oh my GOD!" Hehe...needless to say she felt pretty self-concious about having sex on her period after that, and she was sure to make me feel bad about it by saying, "You scarred me for life!"
I was still able to talk her into it during her periods after that, though.