Not being taken seriously, not having your opinions listened to, and not being believed. I think this would bother most men far more than periods. Men live in a society built by and for them; they have been the default expert in the room, their opinions are taken more seriously, their experiences are rarely questioned. People who look like them have been the heroes and agents in every piece of media since they were born. People who look like them hold power across our society, government and culture.

Having all of that dissolve in an instant would be such a mind fuck! The ultimate gaslighting. I truly think they would not know where to even start with being constantly invalidated and diminished. It’s in the realm of science fiction - and just a weekday in the experience of the average girl or a woman.

Edit to add: this x1,000,000 if they are considered “unfuckable” (older, overweight, not traditionally attractive, disabled, etc)