It's really true. My cycle has synced up with my friends. So we end up menstruating around the same week. Its common for sisters, roommates, friends, mother/daughter, etc.
All I mentioned was that my friends cycles are synced up. At least I didn't give graphic details about it like the mental images these photos about periods give you.
I find that insulting and quite frankly, sexist. I have just as much right to have an opinion about it as you do. You have first hand experience, so instead of just stomping on other people's opinions, why don't you try enlightening them?
It may seem like a lot but it really isn't
Or a very young girl who has yet to experience this hell-bound time of a girl's life.