Out of every taboo thing you could fetishize, why fetishize periods?? Any girl could tell you that between the cramps, moodiness, exhaustion, acne, and period shits, it ain't fun or cute or affirming. It's just an annoying thing that happens every month that you get through with plenty of ibuprofen and tampons.
Although, I'm torn between whether Yaniv's fetish is about periods and they're deluding themselves into pretending their bloody wound is menstruation, or if they just get off to making others uncomfortable. Probably a bit of both.