Grimrock

Just bought this game during the Steam sale, and what's the first thing I do? Collect a ton of custom portraits for my characters.

When you choose the 'import custom portrait' option during character creation, there are buttons for male and female portraits. I can't seem to figure out how to actually sort my mountain of custom portraits by gender. Does anyone know what you have to name the portraits and/or the folder structure required to sort your portraits by gender?

I don't think that button is for sorting the portraits.
From what I understand, the default portrait in the game are hard-coded with a gender, meaning male portrait are assigned as male no matter what.
Custom portrait on the other hand require you to manually select a gender for the portrait. Meaning you could pick a male portrait, but assign it as a female, resulting in a female grunt when the party is hit by an enemy.
So yeah, the button is for assigning a proper gender, not sorting the portraits by gender.

I hope I was able to help.