I realize this isn't a new topic and others have posted before; I simply wanted to report my personal experience.
Without getting into too many details, I hadn't seen my guy in quite a long time and wouldn't you know it that I'd be on my period. In any case, we got together and as things progressed I kept debating if I should go remove my cup and just fess up about being on my period leaving it up to him to see what he wanted to do (I hadn't told him I was on my period and he hadn't yet realized)...I don't mind having intercourse while on my period as long as the guy is okay with it and is the one to keep going and saying he's ok with it otherwise I am too self-conscious about it. The other options were to go remove my cup and use an instead cup I had, just tell him I had my period and didn't want penetrative sex (so I would have essentially been the one automatically rejecting intercourse).
Anyways, I was getting so distracted with all this that I just tried to enjoy the moment and although I was hesitant he ended up trying to penetrate. I finally mentioned he might 'bump' into something...I felt a little silly now!! but he obviously figured out I was on my period (but he didn't know anything about my using a cup). Anyways, he couldn't feel anything and nor could I. Now I was curious, I kept asking him and he kept saying he couldn't feel anything; I was amazed he hadn't even bumped the stem on my cup as it is still intact. I usually also am quite 'tight' down there and expected it would be a tight fit with cup and all. I was so shocked I actually ran off to the bathroom to check if all was well...my cup was still there though the seal had been broken so when I checked for my cup the blood just dripped all over my leg and floor! As I was in the bathroom, no biggie, I cleaned off and well I figured what harm in trying this again, so I reinserted my cup. We had intercourse and the cup didn't interfer in any way. He wasn't able to tell I had anything in there and I couldn't feel it at all; mind you we weren't very aggressive so to speak. We do use condoms and that wasn't a problem either.
I suspect all in all, that the cup wasn't an issue as we were both quite excited and turned on, I had no problems lubricating naturally and we took things relatively slowly. I certainly don't advocate having intercourse with your cup in, but if it does happen and it doesn't hurt or cause discomfort I guess it's okay to keep going. I won't be making it a habit to keep my cup in while having intercourse during my period but I also now know I can just let things happen and not get so distracted with what to do and what to say...I'll just enjoy the moment and let things be and remove the cup if/when needed.