When you (M) look at women in the train or the subway and wish you could look like (/be like) any of them, even the not exactly conventionally good-looking ones.
When having to be you seems like a life-long purgatory. Or like you're living in a "separate but (ha ha!) equal" world, and you're condemned to the less equal side.
When the privileges of being male begin to seem like shackles. And having to put up with the c*** that women suffer every day seems like a more than fair trade-off for not having to be male.