You are correct; I do not menstruate. Thank you for making me publicly out myself. But, the good news is I know some people who do. And so, I feel well poised to answer your questions, and, as you point out, perhaps other menstruators reading this can sound off as well.
For a portion of women, “that time of the month” doesn’t only mean period flow, backaches and more Braxton Family Values than usual, but also a raised level of horniness. I’ve dated some of these women whose need to get laid on or played with far outweighs the “awkwardness” or sanitary consequences of getting busy whilst bleeding.
Now, in terms of masturbating, I can only conclude that a good portion of women who enjoy a regular masturbation practice don’t close shop during their flow. Maybe on the heaviest day, they’ll forgo fingering; maybe if they just put on their fanciest, highest thread count white sheets they’ll skip it; maybe if they don’t feel like washing their hands and crotch, they’ll pass. But just the same, there will be countless nights when a woman finishes watching Drive and says, no amount of blood, or post climax clean up is gonna keep me from my orgasm tonight.
The real question you’re asking is: Is it gross? The real answer is no. Not inherently, but for some yes and for some others sometimes. I’m not expecting a huge comment thread of women admitting their masturbation avec menses habits, but these women readily exist. They exist not in the way Siamese twins and guys with micro penises exist, but more in the way red heads and people with heartburn exist.