Board Thread:General Discussion/@comment-24100805-20160201152915/@comment-32182236-20181127142347

A bandage has been considered protective armor as well, though not nearly effective. It's more effective than a Manly Bandana, sure, but even a stained apron is more effective. A Cowboy Hat is also more effective. (Yes, a cowBOY hat.)

So this isn't evidence of Frisk's gender, but rather, evidence that the standards for "armor" appear to be unrealistically low. Just like Papyrus' standards for dating.

So, once again, Frisk's gender is whatever you choose it to be. You, the player, build Frisk's character. You choose if they're good (Pacifist/Netural) or evil (Genocide), so why not someting as simple as that too?