Ya know, I was a teenaged boy once, and I don’t think we would have been terribly offended by a girl pretending she was a boy so she could share a bathroom with us. Amused, probably, and she might have gotten more of an eyeful than she expected, but I just can’t see any of the guys I knew beating her up for this.
Girls with a guy doing the same, a whole other story, I suspect.
Might have performed an inspection, just to verify what was or wasn’t present.