Woman Tells Boyfriend She'd Date His Twin

It's a truly puzzling matter as to how this woman's confused about her boyfriend and his twin being upset over her sharing that she'd date her boyfriend's twin. I mean, wildly inappropriate, no? We wish this was nothing more than a poorly constructed joke, but it doesn't appear so. Reddit's moral judges in the AITA community have spoken as well, and are in collective agreement that she was in the wrong.